I can share a couple of info and steps to ensure you can take a photo of receipts in your mobile app, @hoopers.
An outdated app may be the root of your account's unexpected behavior. Let’s perform some troubleshooting steps to fix the issue. To start, you’ll want to restart your device.
Once done, refresh the data within the app or from the settings menu. Doing so will reload the application to give a fresh start.
Here's how:
Go to the Hamburger ☰ icon, then select Help & Feedback.
Tap Refresh Data.
Select Refresh.
After that, proceed to your device Settings.
Go to your Settings, and select Setting General iPhone Storage.
Choose an app that will take up a lot of space.
Click the Offload App.
If the issue persists, I suggest uninstalling and reinstalling the mobile app to fix the problem.