How to sign out of my child’s iCloud account on their phone to trade it in?

I am going through the steps provided on the Apple website to erase the content on my child’s phone so that I can trade it in. It will not allow me to sign out of the iCloud account. It says “Sign out is not available due to restrictions”. I don’t have any restrictions set on the phone in the downtime settings. What other restrictions could it be? Anyone else I have this issue and know how to solve it?