None of your suggested steps did anything to resolve the issue. I know it has something to do with either your communications software, or your Payments server software, because otherwise, it wouldn't have been working and then randomly break without any system updates or other changes on the client machines. Further, I would almost guaranty that all of your users are still having the exact same issue. Firstly, the problem is not resolved by contacting the Payments team, because I spent several hours on chat with them yesterday, and they said this problem wasn't fixed yet. By "reopening the investigation," you are basically stating that you decided to resolve an issue that wasn't resolved, and that you really had no way of knowing whether the client issue was actually resolved (it's not). "Verify/Rebuild Data" has nothing to do with this. My file verified without any issues. Also, referring to this as a "minor program issue," is really understating the point a great deal. This is a business-critical feature that you have broken. The application firewall setting did nothing. It wasn't turned on before, and turning it on (or off) with connections for the Quickbooks application allowed does not change the error or the (malfunctioning) operation of the software.
Deleting the eInvoicing keychain entry also does nothing to resolve this issue. Doing that just requires the user to re-log in to the Payments system. The problem obviously isn't with the login functionality. Your users are able to log in and "disconnect" the merchant user account. The problem is clearly with downloading Payment and ACH transaction activity from the Payments server. Any solution that does not resolve that issue is not actually a resolution.
