App issue

Hello there, @Stuart29.

Let's reset your app data so you can raise invoices again in the QuickBooks Online (QBO) mobile app.

Your app may be full of cache. That's why you've experienced some unusual responses from the system. To fix this, I encourage you to clear your app data to refresh the system and remove the older files that cause the issue.

If you're using an Android device, here's how:

1. Go to the More icon at the top right corner of the screen.
2. Choose Settings.
3. Select Refresh Data and choose Yes.

If you're using an iOS device, here's how:

1. Go to the Menu icon at the top left corner of the screen.
2. Choose Help & Feedback.
3. Select Refresh Data and Refresh.

Once you're done, go ahead and open your QBO app to create invoices.

In case the issue persists, I'd recommend uninstalling (tap and hold the app icon) and reinstalling the app. This is to ensure the version you'll be using is updated. 

Also, you may want to check out this article as your reference to guide you about the QBO app features available on supported mobile devices: Compare mobile app features. It contains a comparison chart between Android and iOS devices.

Let me know if you have other concerns about creating and managing invoices in the QBO app. I'm always ready to help. Take care, and have a great day, @Stuart29.