I have not receive any transactions from AMEX in several days. When I try to reset the account I get an HTTP error 400
@4TDS I am not aware of any current widespread American Express connectivity issues. However, an HTTP 400 error during account reset or reauthorization can sometimes indicate a problem with the authorization process rather than with transaction downloads themselves.
A few questions:
Since Quicken uses your default browser during the authorization process, browser-related issues can sometimes interfere with reauthorization. Knowing where in the process the error occurs may help narrow down the cause.
An HTTP error 400 indicates to me that your browser might be at fault here.
I encountered a similar error in one of my Accounts not too long ago and the "fix" here was to make my default browser "Microsoft Edge" instead of "Firefox." After getting that straightened out and the downloading issue solved I switched back to Firefox as my default.