Thanks for getting back to us with additional details, erdooley.

It looks like all possible troubleshooting steps that we can share in the Community has already been provided in this thread. 

In this case, we recommend contacting our phone support team. They' ll double-check everything to determine why you're getting the error even if the Amex account is already added in your Chart of Accounts. 

Here's how:

1. Go to the Help menu and select QuickBooks Desktop Help.
2. Enter Contact us in the Search bar, then press Enter. 
3. Click Contact Us in the bottom part of the page.
4. Select between the chat option or schedule a callback.

Please take note that our phone support line is open from Monday to Friday, in between 6 AM to 4 PM Pacific Tome. They're also open during Saturdays from 6 AM to 1 PM Pacific Time. 

Don't hesitate to visit us again if you need anything else.