Family sharing invitation stuck

I tried to add a new family member. She uses an Android device and has a working Apple ID. The invitation email is received, she click on the invitation link and select the Apple Music app, then accept the terms, then click on Accept (the Accept button turns grey) and signs in with her Apple ID, then fills the authentication code received on a text message, and the nothing happens…. The screen gets stuck in that point forever… no errors, no messages, nothing… and in Apple Family control in my iPhone I still see her status as Invitation Sent.