Family sharing. Only 5 members but Says our family is full.

I’m the family organizer and trying to add a 6th family member, as apple says we should be able to do. However when I send the invitation and its attempted to be accepted we get a message that says our family is full. But we only currently have 5 members in the family sharing, and yes, that includes the organizer.

How can I add the 6th individual?