diff --git a/modules/@shopify/checkout-sheet-kit/android/src/main/java/com/shopify/reactnative/checkoutsheetkit/RCTCheckoutWebView.java b/modules/@shopify/checkout-sheet-kit/android/src/main/java/com/shopify/reactnative/checkoutsheetkit/RCTCheckoutWebView.java
index 512133da..a8d4004f 100644
--- a/modules/@shopify/checkout-sheet-kit/android/src/main/java/com/shopify/reactnative/checkoutsheetkit/RCTCheckoutWebView.java
+++ b/modules/@shopify/checkout-sheet-kit/android/src/main/java/com/shopify/reactnative/checkoutsheetkit/RCTCheckoutWebView.java
@@ -55,6 +55,8 @@ of this software and associated documentation files (the "Software"), to deal
 import com.shopify.checkoutsheetkit.lifecycleevents.CheckoutStartEvent;
 import com.shopify.checkoutsheetkit.rpc.events.CheckoutAddressChangeStart;
 import com.shopify.checkoutsheetkit.rpc.events.CheckoutAddressChangeStartEvent;
+import com.shopify.checkoutsheetkit.rpc.events.CheckoutSubmitStart;
+import com.shopify.checkoutsheetkit.rpc.events.CheckoutSubmitStartEvent;
 
 import com.fasterxml.jackson.core.type.TypeReference;
 import com.fasterxml.jackson.databind.ObjectMapper;
@@ -351,6 +353,26 @@ public void onAddressChangeStart(@NonNull CheckoutAddressChangeStart event) {
       }
     }
 
+    @Override
+    public void onSubmitStart(@NonNull CheckoutSubmitStart event) {
+      try {
+        CheckoutSubmitStartEvent params = event.getParams();
+        Map<String, Object> eventData = new HashMap<>();
+
+        eventData.put("id", event.getId());
+        eventData.put("type", "submitStart");
+        eventData.put("cart", params.getCart());
+
+        Map<String, Object> checkoutData = new HashMap<>();
+        checkoutData.put("id", params.getCheckout().getId());
+        eventData.put("checkout", checkoutData);
+
+        sendEvent("onSubmitStart", serializeToWritableMap(eventData));
+      } catch (Exception e) {
+        Log.e(TAG, "Error processing submit start event", e);
+      }
+    }
+
     @Override
     public void onLinkClick(@NonNull Uri uri) {
       WritableMap params = Arguments.createMap();
diff --git a/modules/@shopify/checkout-sheet-kit/android/src/main/java/com/shopify/reactnative/checkoutsheetkit/RCTCheckoutWebViewManager.java b/modules/@shopify/checkout-sheet-kit/android/src/main/java/com/shopify/reactnative/checkoutsheetkit/RCTCheckoutWebViewManager.java
index 96ac7206..45b7f93d 100644
--- a/modules/@shopify/checkout-sheet-kit/android/src/main/java/com/shopify/reactnative/checkoutsheetkit/RCTCheckoutWebViewManager.java
+++ b/modules/@shopify/checkout-sheet-kit/android/src/main/java/com/shopify/reactnative/checkoutsheetkit/RCTCheckoutWebViewManager.java
@@ -91,6 +91,7 @@ public Map<String, Object> getExportedCustomDirectEventTypeConstants() {
     events.put("onCancel", createEventMap("onCancel"));
     events.put("onLinkClick", createEventMap("onLinkClick"));
     events.put("onAddressChangeStart", createEventMap("onAddressChangeStart"));
+    events.put("onSubmitStart", createEventMap("onSubmitStart"));
     return events;
   }
 
diff --git a/modules/@shopify/checkout-sheet-kit/android/src/main/java/com/shopify/reactnative/checkoutsheetkit/SheetCheckoutEventProcessor.java b/modules/@shopify/checkout-sheet-kit/android/src/main/java/com/shopify/reactnative/checkoutsheetkit/SheetCheckoutEventProcessor.java
index 45a3279e..64ba94bb 100644
--- a/modules/@shopify/checkout-sheet-kit/android/src/main/java/com/shopify/reactnative/checkoutsheetkit/SheetCheckoutEventProcessor.java
+++ b/modules/@shopify/checkout-sheet-kit/android/src/main/java/com/shopify/reactnative/checkoutsheetkit/SheetCheckoutEventProcessor.java
@@ -44,6 +44,8 @@ of this software and associated documentation files (the "Software"), to deal
 import com.shopify.checkoutsheetkit.lifecycleevents.CheckoutStartEvent;
 import com.shopify.checkoutsheetkit.rpc.events.CheckoutAddressChangeStart;
 import com.shopify.checkoutsheetkit.rpc.events.CheckoutAddressChangeStartEvent;
+import com.shopify.checkoutsheetkit.rpc.events.CheckoutSubmitStart;
+import com.shopify.checkoutsheetkit.rpc.events.CheckoutSubmitStartEvent;
 import com.fasterxml.jackson.databind.ObjectMapper;
 
 import java.io.IOException;
@@ -172,6 +174,31 @@ public void onAddressChangeStart(@NonNull CheckoutAddressChangeStart event) {
     }
   }
 
+  @Override
+  public void onSubmitStart(@NonNull CheckoutSubmitStart event) {
+    try {
+      CheckoutSubmitStartEvent params = event.getParams();
+      if (params == null) {
+        Log.e("ShopifyCheckoutSheetKit", "Submit start event has null params");
+        return;
+      }
+
+      Map<String, Object> eventData = new HashMap<>();
+      eventData.put("id", event.getId());
+      eventData.put("type", "submitStart");
+      eventData.put("cart", params.getCart());
+
+      Map<String, Object> checkoutData = new HashMap<>();
+      checkoutData.put("id", params.getCheckout().getId());
+      eventData.put("checkout", checkoutData);
+
+      String data = mapper.writeValueAsString(eventData);
+      sendEventWithStringData("submitStart", data);
+    } catch (IOException e) {
+      Log.e("ShopifyCheckoutSheetKit", "Error processing submit start event", e);
+    }
+  }
+
   // Private
 
   private Map<String, Object> populateErrorDetails(CheckoutException error) {
diff --git a/modules/@shopify/checkout-sheet-kit/ios/RCTCheckoutWebView.swift b/modules/@shopify/checkout-sheet-kit/ios/RCTCheckoutWebView.swift
index 52179437..6548cdb8 100644
--- a/modules/@shopify/checkout-sheet-kit/ios/RCTCheckoutWebView.swift
+++ b/modules/@shopify/checkout-sheet-kit/ios/RCTCheckoutWebView.swift
@@ -85,6 +85,7 @@ class RCTCheckoutWebView: UIView {
   @objc var onLinkClick: RCTBubblingEventBlock?
   @objc var onAddressChangeStart: RCTBubblingEventBlock?
   @objc var onPaymentChangeIntent: RCTBubblingEventBlock?
+  @objc var onSubmitStart: RCTBubblingEventBlock?
 
   override init(frame: CGRect) {
     super.init(frame: frame)
@@ -324,4 +325,30 @@ extension RCTCheckoutWebView: CheckoutDelegate {
 
     onPaymentChangeIntent?(eventData)
   }
+
+  /// Called when the buyer attempts to submit the checkout.
+  ///
+  /// This event is only emitted when native payment delegation is configured
+  /// for the authenticated app.
+  ///
+  /// - Parameter event: The submit start event containing:
+  ///   - id: Unique identifier for responding to the event
+  ///   - cart: Current cart state
+  ///   - checkout: Checkout session information
+  func checkoutDidStartSubmit(event: CheckoutSubmitStart) {
+    guard let id = event.id else { return }
+
+    self.events.set(key: id, event: event)
+
+    let cartJSON = ShopifyEventSerialization.encodeToJSON(from: event.params.cart)
+
+    onSubmitStart?([
+      "id": event.id,
+      "type": "submitStart",
+      "cart": cartJSON,
+      "checkout": [
+        "id": event.params.checkout.id
+      ],
+    ])
+  }
 }
diff --git a/modules/@shopify/checkout-sheet-kit/ios/ShopifyCheckoutSheetKit+EventSerialization.swift b/modules/@shopify/checkout-sheet-kit/ios/ShopifyCheckoutSheetKit+EventSerialization.swift
index a096c89f..e76ca7fe 100644
--- a/modules/@shopify/checkout-sheet-kit/ios/ShopifyCheckoutSheetKit+EventSerialization.swift
+++ b/modules/@shopify/checkout-sheet-kit/ios/ShopifyCheckoutSheetKit+EventSerialization.swift
@@ -85,6 +85,20 @@ internal enum ShopifyEventSerialization {
         ]
     }
 
+    /**
+     * Converts a CheckoutSubmitStart to a React Native compatible dictionary.
+     */
+    static func serialize(checkoutSubmitStart event: CheckoutSubmitStart) -> [String: Any] {
+        return [
+            "id": event.id as Any,
+            "type": "submitStart",
+            "cart": encodeToJSON(from: event.params.cart),
+            "checkout": [
+                "id": event.params.checkout.id
+            ]
+        ]
+    }
+
     static func serialize(clickEvent url: URL) -> [String: URL] {
         return ["url": url]
     }
diff --git a/modules/@shopify/checkout-sheet-kit/ios/ShopifyCheckoutSheetKit.mm b/modules/@shopify/checkout-sheet-kit/ios/ShopifyCheckoutSheetKit.mm
index 873083bb..e6a80e75 100644
--- a/modules/@shopify/checkout-sheet-kit/ios/ShopifyCheckoutSheetKit.mm
+++ b/modules/@shopify/checkout-sheet-kit/ios/ShopifyCheckoutSheetKit.mm
@@ -128,6 +128,11 @@ @interface RCT_EXTERN_MODULE (RCTCheckoutWebViewManager, RCTViewManager)
      */
     RCT_EXPORT_VIEW_PROPERTY(onPaymentChangeIntent, RCTBubblingEventBlock)
 
+    /**
+     * Emitted when the buyer attempts to submit the checkout
+     */
+    RCT_EXPORT_VIEW_PROPERTY(onSubmitStart, RCTBubblingEventBlock)
+
     /**
      * Emitted when a link is clicked
      */
diff --git a/modules/@shopify/checkout-sheet-kit/ios/ShopifyCheckoutSheetKit.swift b/modules/@shopify/checkout-sheet-kit/ios/ShopifyCheckoutSheetKit.swift
index 5e4883a2..5657dd06 100644
--- a/modules/@shopify/checkout-sheet-kit/ios/ShopifyCheckoutSheetKit.swift
+++ b/modules/@shopify/checkout-sheet-kit/ios/ShopifyCheckoutSheetKit.swift
@@ -53,7 +53,7 @@ class RCTShopifyCheckoutSheetKit: RCTEventEmitter, CheckoutDelegate {
     }
 
     override func supportedEvents() -> [String]! {
-        return ["close", "complete", "start", "error", "addressChangeStart"]
+        return ["close", "complete", "start", "error", "addressChangeStart", "submitStart"]
     }
 
     override func startObserving() {
@@ -82,6 +82,12 @@ class RCTShopifyCheckoutSheetKit: RCTEventEmitter, CheckoutDelegate {
         }
     }
 
+    func checkoutDidStartSubmit(event: CheckoutSubmitStart) {
+        if hasListeners {
+            sendEvent(withName: "submitStart", body: ShopifyEventSerialization.serialize(checkoutSubmitStart: event))
+        }
+    }
+
     func shouldRecoverFromError(error: CheckoutError) -> Bool {
         return error.isRecoverable
     }
diff --git a/modules/@shopify/checkout-sheet-kit/src/components/Checkout.tsx b/modules/@shopify/checkout-sheet-kit/src/components/Checkout.tsx
index 194ff601..ef23e98e 100644
--- a/modules/@shopify/checkout-sheet-kit/src/components/Checkout.tsx
+++ b/modules/@shopify/checkout-sheet-kit/src/components/Checkout.tsx
@@ -35,7 +35,11 @@ import type {
   CheckoutException,
 } from '..';
 import {useCheckoutEvents} from '../CheckoutEventProvider';
-import type {CheckoutAddressChangeStart, CheckoutStartEvent} from '../events';
+import type {
+  CheckoutAddressChangeStart,
+  CheckoutStartEvent,
+  CheckoutSubmitStart
+} from '../events';
 
 export interface CheckoutProps {
   /**
@@ -81,6 +85,14 @@ export interface CheckoutProps {
    */
   onAddressChangeStart?: (event: CheckoutAddressChangeStart) => void;
 
+  /**
+   * Called when the buyer attempts to submit the checkout.
+   *
+   * Note: This callback is only invoked when native payment delegation is configured
+   * for the authenticated app.
+   */
+  onSubmitStart?: (event: CheckoutSubmitStart) => void;
+
   /**
    * Style for the webview container
    */
@@ -110,6 +122,7 @@ interface NativeCheckoutWebViewProps {
   onCancel?: () => void;
   onLinkClick?: (event: {nativeEvent: {url: string}}) => void;
   onAddressChangeStart?: (event: {nativeEvent: CheckoutAddressChangeStart}) => void;
+  onSubmitStart?: (event: {nativeEvent: CheckoutSubmitStart}) => void;
 }
 
 const RCTCheckoutWebView =
@@ -167,6 +180,7 @@ export const Checkout = forwardRef<CheckoutRef, CheckoutProps>(
       onCancel,
       onLinkClick,
       onAddressChangeStart,
+      onSubmitStart,
       style,
       testID,
     },
@@ -239,6 +253,16 @@ export const Checkout = forwardRef<CheckoutRef, CheckoutProps>(
       [onAddressChangeStart],
     );
 
+    const handleSubmitStart = useCallback<
+      Required<NativeCheckoutWebViewProps>['onSubmitStart']
+    >(
+      (event: {nativeEvent: CheckoutSubmitStart}) => {
+        if (!event.nativeEvent) return;
+        onSubmitStart?.(event.nativeEvent);
+      },
+      [onSubmitStart],
+    );
+
     const reload = useCallback(() => {
       if (!webViewRef.current) {
         return;
@@ -273,6 +297,7 @@ export const Checkout = forwardRef<CheckoutRef, CheckoutProps>(
         onCancel={handleCancel}
         onLinkClick={handleLinkClick}
         onAddressChangeStart={handleAddressChangeStart}
+        onSubmitStart={handleSubmitStart}
       />
     );
   },
diff --git a/modules/@shopify/checkout-sheet-kit/src/events.d.ts b/modules/@shopify/checkout-sheet-kit/src/events.d.ts
index e2d9f19d..06c29607 100644
--- a/modules/@shopify/checkout-sheet-kit/src/events.d.ts
+++ b/modules/@shopify/checkout-sheet-kit/src/events.d.ts
@@ -379,7 +379,6 @@ export interface CheckoutResponseError {
 
 /**
  * Mailing address input for delivery.
- * Aligns with Storefront API MailingAddressInput.
  *
  * @see https://shopify.dev/docs/api/storefront/latest/input-objects/MailingAddressInput
  */
@@ -428,7 +427,6 @@ export interface CartDeliveryAddressInput {
 
 /**
  * Delivery-related fields for the cart.
- * Aligns with Storefront API CartDeliveryInput.
  *
  * @see https://shopify.dev/docs/api/storefront/latest/input-objects/CartDeliveryInput
  */
@@ -441,7 +439,6 @@ export interface CartDeliveryInput {
 
 /**
  * The customer associated with the cart.
- * Aligns with Storefront API CartBuyerIdentityInput.
  *
  * @see https://shopify.dev/docs/api/storefront/latest/input-objects/CartBuyerIdentityInput
  */
@@ -523,7 +520,7 @@ export interface CheckoutAddressChangeStart {
  */
 export interface CheckoutAddressChangeStartResponse {
   /**
-   * Updated cart input with the delivery address to set.
+   * Updated cart input with the delivery addresses to set.
    */
   cart?: CartInput;
   /**
@@ -548,3 +545,71 @@ export interface CheckoutPaymentChangeIntent {
     brand: string;
   };
 }
+
+/**
+ * Checkout session information.
+ */
+export interface CheckoutSession {
+  /** Globally unique identifier for the checkout session */
+  id: string;
+}
+
+/**
+ * Event emitted when the buyer attempts to submit the checkout.
+ *
+ * This event is only emitted when native payment delegation is configured
+ * for the authenticated app.
+ */
+export interface CheckoutSubmitStart {
+  /**
+   * Unique identifier for this event instance.
+   * Use this ID with the CheckoutEventProvider to respond to the event.
+   */
+  id: string;
+
+  /**
+   * The event type identifier
+   */
+  type: 'submitStart';
+
+  /**
+   * The current cart state when the event was emitted.
+   */
+  cart: Cart;
+
+  /**
+   * The checkout session information.
+   */
+  checkout: CheckoutSession;
+}
+
+/**
+ * Payment token input for delegated payment processing.
+ */
+export interface PaymentTokenInput {
+  token: string;
+  tokenType: string;
+  tokenProvider: string;
+}
+
+/**
+ * Response payload for CheckoutSubmitStart event.
+ * Use with CheckoutEventProvider.respondToEvent() or useShopifyEvent().respondWith()
+ *
+ * Note: This response is only used when native payment delegation is enabled
+ * for the authenticated app.
+ */
+export interface CheckoutSubmitStartResponse {
+  /**
+   * Optional payment token information for delegated payment processing.
+   */
+  payment?: PaymentTokenInput;
+  /**
+   * Updated cart input with delivery addresses and optional buyer identity.
+   */
+  cart?: CartInput;
+  /**
+   * Optional array of errors if the submission failed.
+   */
+  errors?: CheckoutResponseError[];
+}
diff --git a/modules/@shopify/checkout-sheet-kit/src/index.d.ts b/modules/@shopify/checkout-sheet-kit/src/index.d.ts
index c151d356..86d8804c 100644
--- a/modules/@shopify/checkout-sheet-kit/src/index.d.ts
+++ b/modules/@shopify/checkout-sheet-kit/src/index.d.ts
@@ -22,7 +22,7 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SO
 */
 
 import type {EmitterSubscription} from 'react-native';
-import type {CheckoutCompleteEvent, CheckoutStartEvent} from './events';
+import type {CheckoutCompleteEvent, CheckoutStartEvent, CheckoutSubmitStart} from './events';
 import type {CheckoutException} from './errors';
 
 export type Maybe<T> = T | undefined;
@@ -153,6 +153,7 @@ export type CheckoutEvent =
   | 'start'
   | 'error'
   | 'addressChangeStart'
+  | 'submitStart'
   | 'geolocationRequest';
 
 export interface GeolocationRequestEvent {
@@ -173,6 +174,9 @@ export type CheckoutStartEventCallback = (
 export type CheckoutAddressChangeStartCallback = (
   event: CheckoutAddressChangeStart,
 ) => void;
+export type CheckoutSubmitStartCallback = (
+  event: CheckoutSubmitStart,
+) => void;
 
 export type CheckoutEventCallback =
   | CloseEventCallback
@@ -180,6 +184,7 @@ export type CheckoutEventCallback =
   | CheckoutCompleteEventCallback
   | CheckoutStartEventCallback
   | CheckoutAddressChangeStartCallback
+  | CheckoutSubmitStartCallback
   | GeolocationRequestEventCallback;
 
 /**
@@ -263,6 +268,11 @@ function addEventListener(
   callback: CheckoutAddressChangeStartCallback,
 ): Maybe<EmitterSubscription>;
 
+function addEventListener(
+  event: 'submitStart',
+  callback: CheckoutSubmitStartCallback,
+): Maybe<EmitterSubscription>;
+
 function addEventListener(
   event: 'error',
   callback: CheckoutExceptionCallback,
diff --git a/modules/@shopify/checkout-sheet-kit/src/index.ts b/modules/@shopify/checkout-sheet-kit/src/index.ts
index 1898d79d..0e444dcc 100644
--- a/modules/@shopify/checkout-sheet-kit/src/index.ts
+++ b/modules/@shopify/checkout-sheet-kit/src/index.ts
@@ -188,6 +188,9 @@ class ShopifyCheckoutSheet implements ShopifyCheckoutSheetKit {
       case 'addressChangeStart':
         eventCallback = this.interceptEventEmission('addressChangeStart', callback);
         break;
+      case 'submitStart':
+        eventCallback = this.interceptEventEmission('submitStart', callback);
+        break;
       case 'error':
         eventCallback = this.interceptEventEmission(
           'error',
@@ -502,12 +505,16 @@ export type {
   CartDeliveryAddressInput,
   CartDeliveryInput,
   CartInput,
+  PaymentTokenInput,
+  CheckoutSession,
   CheckoutAddressChangeStart,
   CheckoutAddressChangeStartResponse,
   CheckoutCompleteEvent,
   CheckoutPaymentChangeIntent,
   CheckoutResponseError,
   CheckoutStartEvent,
+  CheckoutSubmitStart,
+  CheckoutSubmitStartResponse,
   MailingAddressInput,
 } from './events.d';
 
diff --git a/modules/@shopify/checkout-sheet-kit/tests/CheckoutSubmitStart.test.tsx b/modules/@shopify/checkout-sheet-kit/tests/CheckoutSubmitStart.test.tsx
new file mode 100644
index 00000000..cae80639
--- /dev/null
+++ b/modules/@shopify/checkout-sheet-kit/tests/CheckoutSubmitStart.test.tsx
@@ -0,0 +1,106 @@
+// Mock the native view component BEFORE imports
+jest.mock('react-native', () => {
+  const RN = jest.requireActual('react-native');
+  const React = jest.requireActual('react');
+
+  RN.UIManager.getViewManagerConfig = jest.fn(() => ({
+    Commands: {},
+  }));
+
+  // Create mock component
+  const MockRCTCheckoutWebView = (props: any) => {
+    return React.createElement('View', props);
+  };
+
+  return Object.setPrototypeOf(
+    {
+      requireNativeComponent: jest.fn(() => MockRCTCheckoutWebView),
+    },
+    RN,
+  );
+});
+
+import React from 'react';
+import {render, act} from '@testing-library/react-native';
+import {Checkout} from '../src/components/Checkout';
+import {createTestCart, createTestCheckout} from './testFixtures';
+
+describe('Checkout Component - Submit Start Events', () => {
+  const mockCheckoutUrl = 'https://example.myshopify.com/checkout';
+
+  it('calls onSubmitStart callback with event data', () => {
+    const onSubmitStart = jest.fn();
+
+    const {getByTestId} = render(
+      <Checkout
+        checkoutUrl={mockCheckoutUrl}
+        onSubmitStart={onSubmitStart}
+        testID="checkout-webview"
+      />,
+    );
+
+    const nativeComponent = getByTestId('checkout-webview');
+    const testCart = createTestCart();
+    const testCheckout = createTestCheckout();
+
+    act(() => {
+      nativeComponent.props.onSubmitStart({
+        nativeEvent: {
+          id: 'test-event-123',
+          type: 'submitStart',
+          cart: testCart,
+          checkout: testCheckout,
+        },
+      });
+    });
+
+    expect(onSubmitStart).toHaveBeenCalledTimes(1);
+    expect(onSubmitStart).toHaveBeenCalledWith({
+      id: 'test-event-123',
+      type: 'submitStart',
+      cart: testCart,
+      checkout: testCheckout,
+    });
+  });
+
+  it('does not crash when onSubmitStart prop is not provided', () => {
+    const {getByTestId} = render(
+      <Checkout checkoutUrl={mockCheckoutUrl} testID="checkout-webview" />,
+    );
+
+    const nativeComponent = getByTestId('checkout-webview');
+
+    expect(() => {
+      act(() => {
+        nativeComponent.props.onSubmitStart({
+          nativeEvent: {
+            id: 'test-event',
+            type: 'submitStart',
+            cart: createTestCart(),
+            checkout: createTestCheckout(),
+          },
+        });
+      });
+    }).not.toThrow();
+  });
+
+  it('does not call callback when nativeEvent is missing', () => {
+    const onSubmitStart = jest.fn();
+
+    const {getByTestId} = render(
+      <Checkout
+        checkoutUrl={mockCheckoutUrl}
+        onSubmitStart={onSubmitStart}
+        testID="checkout-webview"
+      />,
+    );
+
+    const nativeComponent = getByTestId('checkout-webview');
+
+    act(() => {
+      nativeComponent.props.onSubmitStart({});
+    });
+
+    expect(onSubmitStart).not.toHaveBeenCalled();
+  });
+});
diff --git a/modules/@shopify/checkout-sheet-kit/tests/index.test.ts b/modules/@shopify/checkout-sheet-kit/tests/index.test.ts
index 9985a77b..3781fa57 100644
--- a/modules/@shopify/checkout-sheet-kit/tests/index.test.ts
+++ b/modules/@shopify/checkout-sheet-kit/tests/index.test.ts
@@ -422,6 +422,42 @@ describe('ShopifyCheckoutSheetKit', () => {
       });
     });
 
+    describe('Submit Start Event', () => {
+      it('parses submitStart event data', () => {
+        const instance = new ShopifyCheckoutSheet();
+        const callback = jest.fn();
+        instance.addEventListener('submitStart', callback);
+
+        eventEmitter.emit('submitStart', {
+          id: 'test-event-id',
+          type: 'submitStart',
+          cart: {id: 'test-cart-id'},
+          checkout: {id: 'checkout-session-123'},
+        });
+
+        expect(callback).toHaveBeenCalledWith({
+          id: 'test-event-id',
+          type: 'submitStart',
+          cart: {id: 'test-cart-id'},
+          checkout: {id: 'checkout-session-123'},
+        });
+      });
+
+      it('prints an error if the submitStart event data cannot be parsed', () => {
+        const mock = jest.spyOn(global.console, 'error');
+        const instance = new ShopifyCheckoutSheet();
+        const callback = jest.fn();
+        instance.addEventListener('submitStart', callback);
+
+        eventEmitter.emit('submitStart', 'INVALID JSON');
+
+        expect(mock).toHaveBeenCalledWith(
+          expect.any(LifecycleEventParseError),
+          'INVALID JSON',
+        );
+      });
+    });
+
     describe('Error Event', () => {
       const internalError = {
         __typename: CheckoutNativeErrorType.InternalError,
diff --git a/modules/@shopify/checkout-sheet-kit/tests/testFixtures.ts b/modules/@shopify/checkout-sheet-kit/tests/testFixtures.ts
index ea1755de..a2174a72 100644
--- a/modules/@shopify/checkout-sheet-kit/tests/testFixtures.ts
+++ b/modules/@shopify/checkout-sheet-kit/tests/testFixtures.ts
@@ -21,7 +21,7 @@ LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
 
-import type {Cart} from '../src/events.d';
+import type {Cart, CheckoutSession} from '../src/events.d';
 
 /**
  * Shared test fixtures for creating test objects.
@@ -73,3 +73,22 @@ export function createTestCart(overrides?: Partial<Cart>): Cart {
   };
 }
 
+/**
+ * Creates a test CheckoutSession instance with sensible defaults.
+ *
+ * @param overrides - Optional partial CheckoutSession object to override defaults
+ * @returns A CheckoutSession instance suitable for testing
+ *
+ * @example
+ * ```typescript
+ * const checkout = createTestCheckout();
+ * const checkoutWithCustomId = createTestCheckout({ id: 'custom-session-id' });
+ * ```
+ */
+export function createTestCheckout(overrides?: Partial<CheckoutSession>): CheckoutSession {
+  return {
+    id: 'checkout-session-123',
+    ...overrides,
+  };
+}
+
diff --git a/sample/src/screens/BuyNow/CheckoutScreen.tsx b/sample/src/screens/BuyNow/CheckoutScreen.tsx
index 73832f6b..3e02cd17 100644
--- a/sample/src/screens/BuyNow/CheckoutScreen.tsx
+++ b/sample/src/screens/BuyNow/CheckoutScreen.tsx
@@ -26,6 +26,8 @@ import {
   type CheckoutCompleteEvent,
   type CheckoutRef,
   type CheckoutStartEvent,
+  type CheckoutSubmitStart,
+  useCheckoutEvents,
 } from '@shopify/checkout-sheet-kit';
 import type {BuyNowStackParamList} from './types';
 import {StyleSheet} from 'react-native';
@@ -37,9 +39,10 @@ export default function CheckoutScreen(props: {
 }) {
   const navigation = useNavigation<NavigationProp<BuyNowStackParamList>>();
   const ref = useRef<CheckoutRef>(null);
+  const eventContext = useCheckoutEvents();
 
-  const onCheckoutStart = (event: CheckoutStartEvent) => {
-    console.log('<CheckoutScreen /> onCheckoutStart: ', event);
+  const onStart = (event: CheckoutStartEvent) => {
+    console.log('<CheckoutScreen /> onStart', event);
   };
 
   const onAddressChangeStart = (event: CheckoutAddressChangeStart) => {
@@ -47,6 +50,21 @@ export default function CheckoutScreen(props: {
     navigation.navigate('Address', {id: event.id});
   };
 
+  const onSubmitStart = async (event: CheckoutSubmitStart) => {
+    console.log('<CheckoutScreen /> onSubmitStart', event);
+    try {
+      await eventContext?.respondToEvent(event.id, {
+        payment: {
+          token: '1234567890',
+          tokenType: 'delegated',
+          tokenProvider: 'shopify',
+        },
+      });
+    } catch (error) {
+      console.error('Failed to respond to submit event:', error);
+    }
+  };
+
   const onCancel = () => {
     console.log('<CheckoutScreen /> onCancel: ');
     navigation.getParent()?.goBack();
@@ -68,8 +86,9 @@ export default function CheckoutScreen(props: {
       checkoutUrl={props.route.params.url}
       auth={props.route.params.auth}
       style={styles.container}
-      onStart={onCheckoutStart}
+      onStart={onStart}
       onAddressChangeStart={onAddressChangeStart}
+      onSubmitStart={onSubmitStart}
       onCancel={onCancel}
       onError={onError}
       onComplete={onComplete}