diff --git a/FirebaseAuth/Sources/Swift/Backend/AuthBackend.swift b/FirebaseAuth/Sources/Swift/Backend/AuthBackend.swift
index 58fb6c4be80..ee0b57f8275 100644
--- a/FirebaseAuth/Sources/Swift/Backend/AuthBackend.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/AuthBackend.swift
@@ -251,66 +251,74 @@ class AuthBackend: AuthBackendProtocol {
     }
     dictionary = decodedDictionary
 
-    var response = T.Response()
+    let responseResult = Result {
+      try T.Response(dictionary: dictionary)
+    }
 
     // At this point we either have an error with successfully decoded
     // details in the body, or we have a response which must pass further
     // validation before we know it's truly successful. We deal with the
     // case where we have an error with successfully decoded error details
     // first:
-    if error != nil {
-      if let errorDictionary = dictionary["error"] as? [String: AnyHashable] {
-        if let errorMessage = errorDictionary["message"] as? String {
-          if let clientError = Self.clientError(
-            withServerErrorMessage: errorMessage,
-            errorDictionary: errorDictionary,
-            response: response,
-            error: error
-          ) {
-            throw clientError
+    switch responseResult {
+    case let .success(response):
+      try propagateError(error, dictionary: dictionary, response: response)
+      // In case returnIDPCredential of a verifyAssertion request is set to
+      // @YES, the server may return a 200 with a response that may contain a
+      // server error.
+      if let verifyAssertionRequest = request as? VerifyAssertionRequest {
+        if verifyAssertionRequest.returnIDPCredential {
+          if let errorMessage = dictionary["errorMessage"] as? String {
+            if let clientError = Self.clientError(
+              withServerErrorMessage: errorMessage,
+              errorDictionary: dictionary,
+              response: response,
+              error: error
+            ) {
+              throw clientError
+            }
           }
         }
-        // Not a message we know, return the message directly.
-        throw AuthErrorUtils.unexpectedErrorResponse(
-          deserializedResponse: errorDictionary,
-          underlyingError: error
-        )
       }
-      // No error message at all, return the decoded response.
+      return response
+    case let .failure(failure):
+      try propagateError(error, dictionary: dictionary, response: nil)
       throw AuthErrorUtils
-        .unexpectedErrorResponse(deserializedResponse: dictionary, underlyingError: error)
+        .RPCResponseDecodingError(deserializedResponse: dictionary, underlyingError: failure)
     }
+  }
 
-    // Finally, we try to populate the response object with the JSON values.
-    do {
-      try response.setFields(dictionary: dictionary)
-    } catch {
-      throw AuthErrorUtils
-        .RPCResponseDecodingError(deserializedResponse: dictionary, underlyingError: error)
+  private func propagateError(_ error: Error?, dictionary: [String: AnyHashable],
+                              response: AuthRPCResponse?) throws {
+    guard let error else {
+      return
     }
-    // In case returnIDPCredential of a verifyAssertion request is set to
-    // @YES, the server may return a 200 with a response that may contain a
-    // server error.
-    if let verifyAssertionRequest = request as? VerifyAssertionRequest {
-      if verifyAssertionRequest.returnIDPCredential {
-        if let errorMessage = dictionary["errorMessage"] as? String {
-          if let clientError = Self.clientError(
-            withServerErrorMessage: errorMessage,
-            errorDictionary: dictionary,
-            response: response,
-            error: error
-          ) {
-            throw clientError
-          }
+
+    if let errorDictionary = dictionary["error"] as? [String: AnyHashable] {
+      if let errorMessage = errorDictionary["message"] as? String {
+        if let clientError = Self.clientError(
+          withServerErrorMessage: errorMessage,
+          errorDictionary: errorDictionary,
+          response: response,
+          error: error
+        ) {
+          throw clientError
         }
       }
+      // Not a message we know, return the message directly.
+      throw AuthErrorUtils.unexpectedErrorResponse(
+        deserializedResponse: errorDictionary,
+        underlyingError: error
+      )
     }
-    return response
+    // No error message at all, return the decoded response.
+    throw AuthErrorUtils
+      .unexpectedErrorResponse(deserializedResponse: dictionary, underlyingError: error)
   }
 
   private static func clientError(withServerErrorMessage serverErrorMessage: String,
                                   errorDictionary: [String: Any],
-                                  response: AuthRPCResponse,
+                                  response: AuthRPCResponse?,
                                   error: Error?) -> Error? {
     let split = serverErrorMessage.split(separator: ":")
     let shortErrorMessage = split.first?.trimmingCharacters(in: .whitespacesAndNewlines)
diff --git a/FirebaseAuth/Sources/Swift/Backend/AuthRPCResponse.swift b/FirebaseAuth/Sources/Swift/Backend/AuthRPCResponse.swift
index 0b7ea8a3a52..00d302e5775 100644
--- a/FirebaseAuth/Sources/Swift/Backend/AuthRPCResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/AuthRPCResponse.swift
@@ -15,14 +15,11 @@
 import Foundation
 
 protocol AuthRPCResponse: Sendable {
-  /// Bare initializer for a response.
-  init()
-
-  /// Sets the response instance from the decoded JSON response.
+  /// Initializes the response instance from the decoded JSON response.
   /// - Parameter dictionary: The dictionary decoded from HTTP JSON response.
   /// - Parameter error: An out field for an error which occurred constructing the request.
   /// - Returns: Whether the operation was successful or not.
-  mutating func setFields(dictionary: [String: AnyHashable]) throws
+  init(dictionary: [String: AnyHashable]) throws
 
   /// This optional method allows response classes to create client errors given a short error
   /// message and a detail error message from the server.
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/CreateAuthURIResponse.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/CreateAuthURIResponse.swift
index 019a92f4b90..66b1ad95023 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/CreateAuthURIResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/CreateAuthURIResponse.swift
@@ -35,7 +35,7 @@ struct CreateAuthURIResponse: AuthRPCResponse {
   /// A list of sign-in methods available for the passed identifier.
   var signinMethods: [String] = []
 
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {
+  init(dictionary: [String: AnyHashable]) throws {
     providerID = dictionary["providerId"] as? String
     authURI = dictionary["authUri"] as? String
     registered = dictionary["registered"] as? Bool ?? false
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/DeleteAccountResponse.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/DeleteAccountResponse.swift
index 4b6802dafb3..d3a34371caa 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/DeleteAccountResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/DeleteAccountResponse.swift
@@ -18,5 +18,5 @@ import Foundation
 ///
 /// See https://developers.google.com/identity/toolkit/web/reference/relyingparty/deleteAccount
 struct DeleteAccountResponse: AuthRPCResponse {
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {}
+  init(dictionary: [String: AnyHashable]) throws {}
 }
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/EmailLinkSignInResponse.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/EmailLinkSignInResponse.swift
index 608c38237cc..0fb80a8f9c2 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/EmailLinkSignInResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/EmailLinkSignInResponse.swift
@@ -40,7 +40,7 @@ struct EmailLinkSignInResponse: AuthRPCResponse, AuthMFAResponse {
   /// Info on which multi-factor authentication providers are enabled.
   private(set) var mfaInfo: [AuthProtoMFAEnrollment]?
 
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {
+  init(dictionary: [String: AnyHashable]) throws {
     email = dictionary["email"] as? String
     idToken = dictionary["idToken"] as? String
     isNewUser = dictionary["isNewUser"] as? Bool ?? false
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/GetAccountInfoResponse.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/GetAccountInfoResponse.swift
index e0f9c463959..4fb5795bcd5 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/GetAccountInfoResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/GetAccountInfoResponse.swift
@@ -139,7 +139,7 @@ struct GetAccountInfoResponse: AuthRPCResponse {
   /// The requested users' profiles.
   var users: [Self.User]?
 
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {
+  init(dictionary: [String: AnyHashable]) throws {
     guard let usersData = dictionary["users"] as? [[String: AnyHashable]] else {
       throw AuthErrorUtils.unexpectedResponse(deserializedResponse: dictionary)
     }
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/GetOOBConfirmationCodeResponse.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/GetOOBConfirmationCodeResponse.swift
index 91721fd659e..dcfba9d5212 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/GetOOBConfirmationCodeResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/GetOOBConfirmationCodeResponse.swift
@@ -19,7 +19,7 @@ private let kOOBCodeKey = "oobCode"
 struct GetOOBConfirmationCodeResponse: AuthRPCResponse {
   var OOBCode: String?
 
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {
+  init(dictionary: [String: AnyHashable]) throws {
     OOBCode = dictionary[kOOBCodeKey] as? String
   }
 }
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/GetProjectConfigResponse.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/GetProjectConfigResponse.swift
index b9fb18771b7..65091a46c7e 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/GetProjectConfigResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/GetProjectConfigResponse.swift
@@ -19,7 +19,7 @@ struct GetProjectConfigResponse: AuthRPCResponse {
 
   var authorizedDomains: [String]?
 
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {
+  init(dictionary: [String: AnyHashable]) throws {
     projectID = dictionary["projectId"] as? String
     if let authorizedDomains = dictionary["authorizedDomains"] as? String,
        let data = authorizedDomains.data(using: .utf8) {
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/GetRecaptchaConfigResponse.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/GetRecaptchaConfigResponse.swift
index b62bd84a695..327ff3751a2 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/GetRecaptchaConfigResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/GetRecaptchaConfigResponse.swift
@@ -18,7 +18,7 @@ struct GetRecaptchaConfigResponse: AuthRPCResponse {
   private(set) var recaptchaKey: String?
   private(set) var enforcementState: [[String: String]]?
 
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {
+  init(dictionary: [String: AnyHashable]) throws {
     recaptchaKey = dictionary["recaptchaKey"] as? String
     enforcementState = dictionary["recaptchaEnforcementState"] as? [[String: String]]
   }
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/MultiFactor/Enroll/FinalizeMFAEnrollmentResponse.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/MultiFactor/Enroll/FinalizeMFAEnrollmentResponse.swift
index bdd3ce89d31..595e3b45952 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/MultiFactor/Enroll/FinalizeMFAEnrollmentResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/MultiFactor/Enroll/FinalizeMFAEnrollmentResponse.swift
@@ -21,7 +21,7 @@ struct FinalizeMFAEnrollmentResponse: AuthRPCResponse {
   private(set) var phoneSessionInfo: AuthProtoFinalizeMFAPhoneResponseInfo?
   private(set) var totpSessionInfo: AuthProtoFinalizeMFATOTPEnrollmentResponseInfo?
 
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {
+  init(dictionary: [String: AnyHashable]) throws {
     idToken = dictionary["idToken"] as? String
     refreshToken = dictionary["refreshToken"] as? String
 
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/MultiFactor/Enroll/StartMFAEnrollmentResponse.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/MultiFactor/Enroll/StartMFAEnrollmentResponse.swift
index dadbb9a15be..7c91b54227c 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/MultiFactor/Enroll/StartMFAEnrollmentResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/MultiFactor/Enroll/StartMFAEnrollmentResponse.swift
@@ -19,7 +19,7 @@ struct StartMFAEnrollmentResponse: AuthRPCResponse {
   private(set) var phoneSessionInfo: AuthProtoStartMFAPhoneResponseInfo?
   private(set) var totpSessionInfo: AuthProtoStartMFATOTPEnrollmentResponseInfo?
 
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {
+  init(dictionary: [String: AnyHashable]) throws {
     if let data = dictionary["phoneSessionInfo"] as? [String: AnyHashable] {
       phoneSessionInfo = AuthProtoStartMFAPhoneResponseInfo(dictionary: data)
     } else if let data = dictionary["totpSessionInfo"] as? [String: AnyHashable] {
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/MultiFactor/SignIn/FinalizeMFASignInResponse.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/MultiFactor/SignIn/FinalizeMFASignInResponse.swift
index 032dab3ff86..850a969e6cd 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/MultiFactor/SignIn/FinalizeMFASignInResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/MultiFactor/SignIn/FinalizeMFASignInResponse.swift
@@ -19,7 +19,7 @@ struct FinalizeMFASignInResponse: AuthRPCResponse {
   var IDToken: String?
   var refreshToken: String?
 
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {
+  init(dictionary: [String: AnyHashable]) throws {
     IDToken = dictionary["idToken"] as? String
     refreshToken = dictionary["refreshToken"] as? String
   }
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/MultiFactor/SignIn/StartMFASignInResponse.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/MultiFactor/SignIn/StartMFASignInResponse.swift
index cc597172010..291821c58f9 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/MultiFactor/SignIn/StartMFASignInResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/MultiFactor/SignIn/StartMFASignInResponse.swift
@@ -18,7 +18,7 @@ import Foundation
 struct StartMFASignInResponse: AuthRPCResponse {
   var responseInfo: AuthProtoStartMFAPhoneResponseInfo?
 
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {
+  init(dictionary: [String: AnyHashable]) throws {
     if let data = dictionary["phoneResponseInfo"] as? [String: AnyHashable] {
       responseInfo = AuthProtoStartMFAPhoneResponseInfo(dictionary: data)
     } else {
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/MultiFactor/Unenroll/WithdrawMFAResponse.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/MultiFactor/Unenroll/WithdrawMFAResponse.swift
index 4744a6965ee..27bcd0d32e4 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/MultiFactor/Unenroll/WithdrawMFAResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/MultiFactor/Unenroll/WithdrawMFAResponse.swift
@@ -18,7 +18,7 @@ struct WithdrawMFAResponse: AuthRPCResponse {
   var idToken: String?
   var refreshToken: String?
 
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {
+  init(dictionary: [String: AnyHashable]) throws {
     idToken = dictionary["idToken"] as? String
     refreshToken = dictionary["refreshToken"] as? String
   }
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/ResetPasswordResponse.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/ResetPasswordResponse.swift
index 22cb703e5ad..1744dfc34cf 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/ResetPasswordResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/ResetPasswordResponse.swift
@@ -34,7 +34,7 @@ struct ResetPasswordResponse: AuthRPCResponse {
   /// The type of request as returned by the backend.
   var requestType: String?
 
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {
+  init(dictionary: [String: AnyHashable]) throws {
     email = dictionary["email"] as? String
     requestType = dictionary["requestType"] as? String
     verifiedEmail = dictionary["newEmail"] as? String
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/RevokeTokenResponse.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/RevokeTokenResponse.swift
index 7e6bf0e7378..900959ccbe1 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/RevokeTokenResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/RevokeTokenResponse.swift
@@ -15,7 +15,7 @@
 import Foundation
 
 struct RevokeTokenResponse: AuthRPCResponse {
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {
+  init(dictionary: [String: AnyHashable]) throws {
     // Nothing to set or throw.
   }
 }
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/SecureTokenResponse.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/SecureTokenResponse.swift
index 86291a60015..44409ba92d4 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/SecureTokenResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/SecureTokenResponse.swift
@@ -37,7 +37,7 @@ struct SecureTokenResponse: AuthRPCResponse {
 
   var expectedKind: String? { nil }
 
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {
+  init(dictionary: [String: AnyHashable]) throws {
     refreshToken = dictionary[kRefreshTokenKey] as? String
     self.accessToken = dictionary[kAccessTokenKey] as? String
     idToken = dictionary[kIDTokenKey] as? String
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/SendVerificationTokenResponse.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/SendVerificationTokenResponse.swift
index f9e6872cfcb..7b1815c5925 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/SendVerificationTokenResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/SendVerificationTokenResponse.swift
@@ -17,7 +17,7 @@ import Foundation
 struct SendVerificationCodeResponse: AuthRPCResponse {
   var verificationID: String?
 
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {
+  init(dictionary: [String: AnyHashable]) throws {
     verificationID = dictionary["sessionInfo"] as? String
   }
 }
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/SetAccountInfoResponse.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/SetAccountInfoResponse.swift
index c1b932b83c2..0a036d95195 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/SetAccountInfoResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/SetAccountInfoResponse.swift
@@ -60,7 +60,7 @@ struct SetAccountInfoResponse: AuthRPCResponse {
   /// The refresh token from Secure Token Service.
   var refreshToken: String?
 
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {
+  init(dictionary: [String: AnyHashable]) throws {
     email = dictionary["email"] as? String
     displayName = dictionary["displayName"] as? String
     idToken = dictionary["idToken"] as? String
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/SignInWithGameCenterResponse.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/SignInWithGameCenterResponse.swift
index d291384ff49..cc81610b17b 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/SignInWithGameCenterResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/SignInWithGameCenterResponse.swift
@@ -25,7 +25,7 @@ struct SignInWithGameCenterResponse: AuthRPCResponse {
   var isNewUser: Bool = false
   var displayName: String?
 
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {
+  init(dictionary: [String: AnyHashable]) throws {
     idToken = dictionary["idToken"] as? String
     refreshToken = dictionary["refreshToken"] as? String
     localID = dictionary["localId"] as? String
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/SignUpNewUserResponse.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/SignUpNewUserResponse.swift
index 7b25c6a6f8c..21f359b0f1a 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/SignUpNewUserResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/SignUpNewUserResponse.swift
@@ -26,7 +26,7 @@ struct SignUpNewUserResponse: AuthRPCResponse {
   /// The refresh token from Secure Token Service.
   var refreshToken: String?
 
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {
+  init(dictionary: [String: AnyHashable]) throws {
     idToken = dictionary["idToken"] as? String
     if let approximateExpirationDate = dictionary["expiresIn"] as? String {
       self
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/VerifyAssertionResponse.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/VerifyAssertionResponse.swift
index 9cf822cae0e..30e10d27336 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/VerifyAssertionResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/VerifyAssertionResponse.swift
@@ -132,7 +132,7 @@ struct VerifyAssertionResponse: AuthRPCResponse, AuthMFAResponse {
 
   private(set) var mfaInfo: [AuthProtoMFAEnrollment]?
 
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {
+  init(dictionary: [String: AnyHashable]) throws {
     federatedID = dictionary["federatedId"] as? String
     providerID = dictionary["providerId"] as? String
     localID = dictionary["localId"] as? String
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/VerifyCustomTokenResponse.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/VerifyCustomTokenResponse.swift
index 5c66bf6ba74..9cf1ec0924f 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/VerifyCustomTokenResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/VerifyCustomTokenResponse.swift
@@ -30,7 +30,7 @@ struct VerifyCustomTokenResponse: AuthRPCResponse {
   /// Flag indicating that the user signing in is a new user and not a returning user.
   var isNewUser: Bool = false
 
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {
+  init(dictionary: [String: AnyHashable]) throws {
     idToken = dictionary["idToken"] as? String
     if let dateString = dictionary["expiresIn"] as? NSString {
       approximateExpirationDate = Date(timeIntervalSinceNow: dateString.doubleValue)
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/VerifyPasswordResponse.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/VerifyPasswordResponse.swift
index ba93ac1e0a5..22a3d87e958 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/VerifyPasswordResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/VerifyPasswordResponse.swift
@@ -51,7 +51,7 @@ struct VerifyPasswordResponse: AuthRPCResponse, AuthMFAResponse {
 
   private(set) var mfaInfo: [AuthProtoMFAEnrollment]?
 
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {
+  init(dictionary: [String: AnyHashable]) throws {
     localID = dictionary["localId"] as? String
     email = dictionary["email"] as? String
     displayName = dictionary["displayName"] as? String
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/VerifyPhoneNumberResponse.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/VerifyPhoneNumberResponse.swift
index b5efb964c73..a187824b7dd 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/VerifyPhoneNumberResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/VerifyPhoneNumberResponse.swift
@@ -43,7 +43,7 @@ struct VerifyPhoneNumberResponse: AuthRPCResponse {
     nil
   }
 
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {
+  init(dictionary: [String: AnyHashable]) throws {
     idToken = dictionary["idToken"] as? String
     refreshToken = dictionary["refreshToken"] as? String
     isNewUser = (dictionary["isNewUser"] as? Bool) ?? false
diff --git a/FirebaseAuth/Sources/Swift/Backend/VerifyClientResponse.swift b/FirebaseAuth/Sources/Swift/Backend/VerifyClientResponse.swift
index 683ed33a01f..a468197948f 100644
--- a/FirebaseAuth/Sources/Swift/Backend/VerifyClientResponse.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/VerifyClientResponse.swift
@@ -15,15 +15,13 @@
 import Foundation
 
 struct VerifyClientResponse: AuthRPCResponse {
-  init() {}
-
   /// Receipt that the APNS token was successfully validated with APNS.
   private(set) var receipt: String?
 
   /// The date after which delivery of the silent push notification is considered to have failed.
   private(set) var suggestedTimeOutDate: Date?
 
-  mutating func setFields(dictionary: [String: AnyHashable]) throws {
+  init(dictionary: [String: AnyHashable]) throws {
     receipt = dictionary["receipt"] as? String
     let suggestedTimeout = dictionary["suggestedTimeout"]
     if let string = suggestedTimeout as? String,
diff --git a/FirebaseAuth/Tests/Unit/AuthBackendTests.swift b/FirebaseAuth/Tests/Unit/AuthBackendTests.swift
index a7a484a7d5d..b163d34ea68 100644
--- a/FirebaseAuth/Tests/Unit/AuthBackendTests.swift
+++ b/FirebaseAuth/Tests/Unit/AuthBackendTests.swift
@@ -713,7 +713,7 @@ class AuthBackendTests: RPCBaseTests {
 
   private struct FakeResponse: AuthRPCResponse {
     var receivedValue: String?
-    mutating func setFields(dictionary: [String: AnyHashable]) throws {
+    init(dictionary: [String: AnyHashable]) throws {
       receivedValue = dictionary["TestKey"] as? String
     }
   }
@@ -739,7 +739,7 @@ class AuthBackendTests: RPCBaseTests {
   }
 
   private struct FakeDecodingErrorResponse: AuthRPCResponse {
-    mutating func setFields(dictionary: [String: AnyHashable]) throws {
+    init(dictionary: [String: AnyHashable]) throws {
       throw NSError(domain: "dummy", code: -1)
     }
   }