Secure Folder

[ClaireLRB069]

My child has Galaxy S21 Ultra phone and we are trying to activate the Secure Folder app. Have followed the Samsung instructions up to step 6 but when we press 'continue' we get a message stating "If this keeps happening, contact Customer Service". What do we do? 

They have my old hand-me-down-phone, Parental Controls are managed via Google Family Link through choice, although they are 13 and we are giving parental permission for this but cannot figure it out.

Grateful for any help you can offer