I can't update any expenses or transactions on the app, when I try to it says "new info exists" and then won't save the update, happening on both my iPad and iPhone

Hello there, slookner. I appreciate you for bringing this issue to our attention.

I'm here to help you update your transactions while using your iPad or iPhone.

Beforehand, let's ensure that you're using supported mobile operating systems. For iPhone and iPad devices, it must be running an IOS 11.1. You can check our system requirements for QuickBooks Online, Accountant, Payroll, and QuickBooks Self-Employed as this helps your application work continuously without interruptions.

On the other hand, you can also reset the app's cache for you to be able to refresh the connection. I'd be glad to show you how:

1. Go to Settings and click Setting General iPad Storage.
2. Choose an app that's taking up a lot of space.
3. To free up the storage without deleting the documents and data for the app, hit the Offload App.

Once everything's settled, you can then check if you're now able to update your transactions. If the issue persists, you can uninstall and reinstall the app.

Alternatively, you can also access your QuickBooks account via browser to update your transactions.

Lastly, I've added this article that you can browse through in case you need assistance entering past transactions in QBO: Manually import transactions in QuickBooks Online. 

Please know that you're always welcome to reach out for further inquiries about managing and tracking your transactions. I'd be glad to assist you 24/7. Stay safe!