[AcceleratedCheckout] Double tapping on Apple Pay makes the app crash

[thib4ult]

What area is the issue related to?

Checkout Sheet Kit

What version of Checkout Sheet Kit are you using?

3.4.0

Reproducible sample code

Double tapping on Apple Pay makes the app crash

Steps to Reproduce

We're using AcceleratedCheckoutButtons to display the Apple Pay button like this :

AcceleratedCheckoutButtons(cartID: temporaryCartId)
					.applePayLabel(.plain)
					.wallets([.applePay])
					.payWithApplePayButtonStyle(.black)

If you tap real fast multiple time on the Apple Pay button, the ApplePayViewController calls the function func onPress() async { multiple time and the SDK crashes.

Expected Behavior

The app/SDK shouldn't crash

Actual Behavior

The app crashes if you tap multiple time on the Apple Pay button.

Screenshots/Videos/Log output

No response

Storefront domain

fahlo-dev-v2.myshopify.com

[kieran-osgood-shopify]

Hey @thib4ult

Thanks for the report - I just tried to reproduce this and couldn't get a crash
Before we can look into this could you create a reproduction or share the stack trace of the crash so we can see the source of the crash

[thib4ult]

Hey @kieran-osgood-shopify

For sure, here is my sentry report of the error :

EXC_BREAKPOINT: BUG IN CLIENT OF LIBDISPATCH: Assertion failed: Block was expected to execute on queue [com.apple.main-thread (0x207718500)] > com.apple.main-thread > SwiftUI.AppSceneDelegate

Issue Summary

Main Thread Assertion Failure During Apple Pay Flow
What's wrong: EXC_BREAKPOINT due to dispatch assertion failure on main-thread.
In the trace: Crash occurred immediately after Apple Pay button tap and related GraphQL POST.
Possible cause: Concurrency violation: A block expected on SwiftUI.AppSceneDelegate's main thread was executed elsewhere, possibly from the ApplePayViewController logic.

Tags

• app.device: d5d77f3bea9b533406c07038b13d0d4ef76624ae
• device: iPhone16,2
• device.class: high
• device.family: iOS
• dist: 1330
• environment: demo
• handled: no
• level: fatal
• mechanism: mach
• os: iOS 26.0
• os.build: 23A341
• os.name: iOS
• os.rooted: no

Exception

Exception 1

Type: EXC_BREAKPOINT
Value: BUG IN CLIENT OF LIBDISPATCH: Assertion failed: Block was expected to execute on queue [com.apple.main-thread (0x207718500)] > com.apple.main-thread > SwiftUI.AppSceneDelegate

Stacktrace

 _dispatch_assert_queue_fail in unknown file [Line null] (Not in app)
 dispatch_assert_queue$V2.cold.1 in unknown file [Line null] (Not in app)
 dispatch_assert_queue in unknown file [Line null] (Not in app)
 _swift_task_checkIsolatedSwift in unknown file [Line null] (Not in app)
 swift_task_isCurrentExecutorWithFlagsImpl in unknown file [Line null] (Not in app)
 closure in ShopPDPAddToCartView.addToCartView.getter in ShopPDPAddToCartView.swift [Line null] (In app)
 ApplePayViewController.onPress in ApplePayViewController.swift [Line 165] (In app)
 swift::runJobInEstablishedExecutorContext in unknown file [Line null] (Not in app)

Thread: Thread 24 (crashed)

Stacktrace

 _dispatch_assert_queue_fail in unknown file [Line null] (Not in app)
 dispatch_assert_queue$V2.cold.1 in unknown file [Line null] (Not in app)
 dispatch_assert_queue in unknown file [Line null] (Not in app)
 _swift_task_checkIsolatedSwift in unknown file [Line null] (Not in app)
 swift_task_isCurrentExecutorWithFlagsImpl in unknown file [Line null] (Not in app)
 closure in ShopPDPAddToCartView.addToCartView.getter in ShopPDPAddToCartView.swift [Line null] (In app)
 ApplePayViewController.onPress in ApplePayViewController.swift [Line 165] (In app)
 swift::runJobInEstablishedExecutorContext in unknown file [Line null] (Not in app)

From what I can see, if you tap the button twice or more, before the applePay sheet gets open : the first tap triggers the sheet properly. The second tap fails and call the callback onCheckoutFailed (line 165 in the ApplePayViewController file) and that creates the crash.

We can reproduce it 100% of the time.

[kieran-osgood-shopify]

Thanks - thats useful information

I still can't manage to reproduce this just yet but have some follow ups after toying around with things

Questions:

1. Are you compiling your app with Swift 6 language mode?
2. Do your network logs contain anything of interest to understand what the condition of the first and second calls were? (did they all succeed, some failures?)
3. If you enable verbose logging can you share a log file (Increase verbosity during development with ShopifyAcceleratedCheckouts.logLevel = .all and ShopifyCheckoutSheetKit.configuration.logLevel = .all.)
4. If you were to pull down the sample app we have: https://github.com/Shopify/checkout-sheet-kit-swift/tree/main/Samples/MobileBuyIntegration does it fail for you here?

If you aren't able to replicate in the sample app and are using Swift 5 we might need a reproduction to narrow things down further

[thib4ult]

1. We're using swift 6
   2.-3. there is probably something interesting in the logs, but it really doesn't help me to resolve this :

[ShopifyAcceleratedCheckouts] (Debug) - ApplePayState: startPaymentRequest -> appleSheetPresented
[ShopifyAcceleratedCheckouts] (Error) - InvalidStateTransitionError: appleSheetPresented -> startPaymentRequest
[ShopifyAcceleratedCheckouts] (Error) - [startPayment] Failed to setup cart: InvalidStateTransitionError(fromState: ShopifyAcceleratedCheckouts.ApplePayState.appleSheetPresented, toState: ShopifyAcceleratedCheckouts.ApplePayState.startPaymentRequest)

and obviously the errors are happening only if you double/triple tap on the button.

4. I'm not able to reproduce that crash within the sample app, which is quite interesting since the implementation is the same in my app and the sample one.

[kieran-osgood-shopify]

Appreciate you doing all that leg work - I think all of this supports my hunch

Our library and sample app runs on Swift 5

As of this moment we don't support Swift 6 concurrency safety features yet

I was under the impression the library wouldn't compile under Swift 6 language mode but seems that only applies to Application level code, and there can be runtime assertions failed by our SDK

---

It's in our roadmap and I hope to get it prioritised but currently don't have any timelines on that

[kieran-osgood-shopify]

Leaving this open until I make the release to npm
The underlying Swift PR that fixes this behaviour is merged and I'll be releasing Swift 3.5.0 tomorrow

[kieran-osgood-shopify]

3.5.0 has been released so I will close this as complete
If you find its still happening please reply here and we can re-open