GTA Online Bug to join a friend?

Hello, my friend just started GTA Online and he is alone in a session, he can't join me and I can't join him either. Maybe he needs to do something like a mission before he can join? No matter if he accepts the invitations, it loads for him and sends him some sort of error message.
(The problem doesn't come from his connection or mine).
If you have a way to help us, please.