I cannot add myself as a TestFlight user to my own app. When I open the invite link on my device, or manually enter the redeem code on device (obtained from opening the invite link on macOS), I get "This invitation has been revoked or is invalid".
I've tried going to App Store Connect and removing myself from both the testing group and the list of 'All testers', both to no avail.
Apple folks: this is not user error and you must have thousands of bug reports on this by now. Why don't you prioritize a fix for this incredibly annoying issue?