Unable to Join Apple Music through Family Sharing invite

To join a Family with a Family Music subscription (not just an individual subscription):

After accepting the invitation and being added to Family Sharing by the family organiser, you automatically have access. Everyone has their own Music Library to which they can add music of their own choice:

Check you are signed in (to your iPhone) with your correct Apple ID:

Sign in with your Apple ID - Apple Support

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On your iPhone, iPad, iPod touch or Android device

1. 1. Open the Apple Music app and tap Listen Now.
   2. In the upper-right corner, tap the photo icon.
   3. Sign in with your Apple ID and password.

Above is from: Join Apple Music - Apple Support

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Any previous purchases may be available in the "Library" in the Music app.

or

If needed:

How to: Redownload music - Apple Support

and

How to: Add and download music from Apple Music - Apple Support

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What to do: If you can't find your family's shared apps and content - Apple Support

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If needed: Music Support Website (info. / support / contact options:

Music - Official Apple Support