It's telling me that I need to purchase a Nintendo Switch Online membership even though I have one already.

The Nintendo Account you used to sign into Nintendo Music may not have an active Nintendo Switch Online membership associated with it.
Try signing out of Nintendo Music and signing in with a different Nintendo Account that has an active Nintendo Switch Online membership.

Please visit the following link for instructions on how to sign out.

• How do I sign out of Nintendo Music?

To view your Nintendo Account's Nintendo Switch Online status, follow these steps:

1. Visit https://accounts.nintendo.com/portal
2. Click "Nintendo Switch Online".
3. Check your Valid Memberships.

If it states you do not have an active Nintendo Switch Online membership, please sign in with a different Nintendo Account and check the membership status of that account.

*The Nintendo Account you are logged into on your browser may be different from the one you have used for Nintendo Music.