I understand you've been through a lot with the problems you encounter using the iPhone app, @Willie A.
I want to help in any way I can regarding the invoice issues you mentioned.
There are similar cases from other users who are encountering The quantity is larger than the maximum allowed error. This issue can be sorted out by uninstalling and reinstalling the app. This will refresh the connection between your app and your mobile.
Here's how to reinstall:
Open the App Store on your device and search for QuickBooks Online.
Click Free and then Install.
Sign in using the same user ID and password that you used when you signed up for QBO.
For the email address issue, you can only use an email that doesn't exceed 40 characters limit. If the email address is too long, it'd be best to use another email.
However, if these issues persist, I'd suggest reaching out to our Online Support so they can isolate this further. They can open an investigation and escalate this if needed.
I'll be around to help if you have additional questions about using your QuickBooks App. I want to ensure this is taken care of so please keep me posted with the results.