cant add a family member with existing spotify account

[lcollin3]

Good morning,

I've had a spotify family account for several months, but can't seem to add my son, who has an existing spotify account that he wants to link.  I was able to add the other family members without accounts with no problem.  When my son follows the invitation link and completes the address information it says that he cannot be added to the family package, even though we all live at the same address. Im sure Im missing something.  Any thoughts for how to add him?  He doesn't want to loose his account because he has already added playlists, etc. Thanks!