TestFlight - Restore not working - "An unknown error has occurred."

In TestFlight, when I restore, I get the message "An unknown error has occurred."

It is working fine in SandBox.

In the App Delegate, I changed the line config.setEnvironment(.sandbox) to config.setEnvironment(.production). I uploaded the App for Distribution.

Once, I was able to make a single purchase with TestFlight. However, the restore error message came back again. I even tried using a SandBox account in TestFlight. That didn't work either.

Does anyone have any ideas?

Thanks