I'm developing an iOS app for a client. I attempt to add him as a user under "Users and Access" using his apple ID email address. He receives the invite and enters his apple ID and password, but receives this error message:
"Unable to Sign In" - "This app is used by developers to manage apps on the App Store. To get access, ask your Account Holder to set up an App Store Connect account for you. (2002)"
Under Users and Access, the user record is grayed out as though he hasn't accepted the invitation, and I can't add him as a tester in the app yet.