My husband is listed as a child on the smart family app even though he is listed as a manager on the account. I am unable to change him to parent even though the instructions say to make them a manager first. He already is and I still can’t change it.
Make sure his number is listed on the account manager screen. I had this same issue with my wife. Her name and email was listed, but not her number. I updated to include her number and was able to add her as a parent in the app.