Our goal is to make QuickBooks Online as easy and user-friendly as it can be, while allowing you to connect to the bank feed, process online payments, and process the payment for your subscription in a way that's convenient for you.
You can use an American Express credit card to pay for your subscription, as well as sync to the bank feed. You're unable to accept online payments (via QuickBooks Online Payments) with American Express. When using QuickBooks Online Payments, you're able to accept Visa, MasterCard, Apple Pay, and Discover.
I hope this helps answer your question. If you have any other questions about American Express and QuickBooks Online, please don't hesitate to reach out.