Cannot start family sharing: Apple id is already used for shared purchases

Question

I'm trying to set-up family sharing on multiple devices, but I'm informed that my mac.com address is "already used for shared purchases" and "accounts can only be part of one Family at a time" with a dialogue box of "OK". We are only one family, and all devices were recently under my iTunes/Apple account. How do I change that so that I can set up family sharing? I have an 11 year old itching for her own phone and want to be able to share, but also to manually approve purchases (which I think is the point of family sharing, especially with someone under 13.)

Answer 1

I FIGURED THIS ONE OUT!!!  What happened was initially I had set up a Family Sharing account under my wife's old iCloud login (old email address) .  I had set her up as the administrator of the account.  We used MY credit card info to handle any purchases made.
Some time later we decided to share MY iCloud account rather than having separate accounts (thus, same email for iCloud login).  While switching her out of her old iCloud login over to sharing my login, it never crossed my mind that I had used her old iCloud login to set up Family Sharing.  Since her old iCloud login was set up as the administrator of the account, all I had to do was sign into iCloud with her old email address and password that she had used before.  Once logged in, I went to Family Sharing and chose an option to stop Family Sharing.  As soon as I did that, I re-logged in with the new shared iCloud account and was able to immediately set up Family Sharing.  Phew!!!
Hope this helps