Can anyone advise on why Amex Credit Card feeds have stopped working since 1st April?

Welcome and thanks for posting in the Community, @alan29.

We are upgrading our bank feeds to comply with the new Open Banking  regulations. There are financial institutions (FI) that don't have this feature available yet, including American Express.

In compliance with this regulation, the connections for the bank feeds in these instances are now turned off. Though we are working closely with the bank to have this implemented in the coming months.

For more information, consider checking out this article: Understanding if you can upgrade your bank feeds to Open Banking. In the meantime, you can manually upload transactions into QuickBooks Online (QBO) as a workaround.

Reach out to me in the comment section below if you have any other questions or concerns, and I'll get back to you right away. I'll be here to help. Have a good one!