Same issue here, Can't create Sandbox Testers spits out the error in the console Network tab the response:
{
"errors": [{
"status": "500",
"code": "UNEXPECTED_ERROR",
"title": "An unexpected error occurred.",
"detail": "An unexpected error occurred on the server side. If this issue continues, contact us at https://developer.apple.com/contact/."
}]
}
What's going on ?
Thanks in advance