Family invite works for new accounts, doesn't for existing

[user-removed]

Since i upgraded to spotify premium family some months ago i would really like to actually invite my wife to this account. 

That's not possible, all i could get the last 20 times i tried was a "Something went wrong" message. 

Using a fresh account (look out for johannhartmann+spotify+hates+customers@... in your database) it works perfectly well, it just doesn't with the existing free account of my wife. Same adress when registering for family invite, of course. 

best, 

johann