I recognize the importance of your snap receipts, Simon. Let's work together and narrow the track by executing troubleshooting steps to resolve this promptly.

Let's start by clearing your app's cache to refresh the data. This process can eliminate stored cache that may cause unusual system behavior. I'll provide different steps for Android and iOS devices.

• For Android:

1. Go to the Gear icon at the top right.
2. Choose Settings.
3. Then, click Refresh Data and tap Yes.

• For iOS:

1. Click the Menu button at the lower right corner.
2. Go to the Gear Icon.
3. Select Refresh Data and click Refresh.

 
After clearing the cache, try snapping a receipt again to see if it works. If the issue persists, uninstall and reinstall the application for a fresh start.  I'll show you how:

• For Android

1. Open the Google Play Store app.
2. Click the menu, then choose My Apps & games.
3. Tap on the QuickBooks Online (QBO) mobile app.
4. Select Uninstall.

• For iOS

1. Look for your QBO app on the home page.
2. Hold the app for 3 seconds. Once an X button appears at the upper right of the app, click it. 
3. Choose Uninstall, then click Yes to confirm.

After that, reinstall the QBO mobile app for both Android and iOS. This also provides a link for mobile devices that support the application.

You can refer to this article for more troubleshooting methods you can execute: Fix common errors in the QuickBooks Online mobile app for Android.
 
Additionally, check out this material that discusses linking sales receipts with expense transactions: Attach receipts to expenses in the QuickBooks Online mobile app.

Let me know how the troubleshooting goes by returning to this thread and adding further information. I'll keep an eye out. Keep safe!