Family Sharing setup was never completed but can’t set it up now

A few months ago, I was exploring the Family Sharing options, and I exited without actually completing the setup.

Now, every time I try to return to set up Family Sharing, I get an error message that reads:

Cannot Start Family Sharing

“xxxx@xxxx.com” is already used for shared purchases in X’s family. Ask X to send you an invitation to join Family Sharing.

The problem is that I am X, and I am signed into iCloud. The same thing happens on all devices (mac, iPhone, iPad) and it doesn’t matter if I sign out of iCloud and then back in.

Anyone have any ideas what might be happening and how to fix it?