Hi there for some reason I can’t open my invoices or make invoices on my mobile devices why

Allow me to provide you with troubleshooting steps to narrow down the cause, @uservicnjay.

There are instances when the app has a large amount of data, resulting in strange results. You can fix this by clearing the app's cache.

Here's how: 

iOS

1. Go to Menu ☰ and tap Help & Feedback.
2. Tap Refresh Data.
3. Note: A message appears Caution. If there was a problem getting your latest QuickBooks Online data, you can refresh it now. It may take a few minutes.
4. Tap Refresh to confirm.

Andriod

1. Go to Menu ☰, then tap More Options.
2. Tap the Settings and Refresh Data.
3. Tap YES to confirm.

By doing this, it'll refresh the huge amount of data stored in your cache.

However, if the issue persists, I recommend uninstalling and reinstalling the application as an alternative solution.

In addition, let me leave this article for your reference to learn how to delete browser cache and Intuit-specific cookies in QuickBooks Online: Clear cache and cookies to fix issues when using QuickBooks Online.

Should you need further assistance, feel free to leave a comment. I'll be on the lookout. Stay safe.