hello, still got slot available ??
can transfer immediately, thanks

u got pmed

So, I successfully added another person in my plan, but it was not easy.
I faced the issue Find another Premium plan that's right for you

What I did was:
Login to their account on my device and play some music for a few minutes (just to match our IP addresses)
Then contact support asking them why I can't add them. They'll check and tell you that they'll email you in a few days (I got the email the next day of contacting them)

In the email they'll say "after review bla3 you can now add them"
So just login back to their account on your device, to once again match the IP with yours, and you can successfully add them to the family plan.

Good luck to everyone who's facing the same issue. And to those that are looking to join another family plan, I suggest to not do it as it's too much of a hassle to redo all those steps.

UPDATE: FULL

PM me with your phone number or ask for mine; so i can add you to the spotify family group formed since 2022 and on the legacy plan (6 slots).

also apparently i read the others having issue adding user to the plan ? i added a friend of mine recently that was not on any premium before without issue, so maybe just create a new account with all your playlist imported from the old account before attempt applying for a spotify family pack slot