@Anonymous-

Thank you for your response. I've also tried this method, but when I attempt to sign into my AMEX account to add a new account, I get a new error message...

[OLSU-1011] QuickBooks couldn't access the branding and profile servers. Find common fixes for the issue or verify your credentials and try again.

This error pops up before I even attempt to sign into my AMEX account, right after I click on the "American Express" option to add an account. I have also tried all the common fixes that the error message links to.