I'm trying to add a child account and it is not letting me. I need help.

Trying to add a child account (got her a used iPhone). Using my MacBook Air (Big Sur) to set up the account since it won't let me do on her iPhone. In my account, I've enabled Family Sharing. I select to add an account, and then in the invitation popup I select "create child account' and the subsequent pop up (Parental Consent) gives options: "learn more", "cancel", and "Go to App Store". I have gone through the App Store to ensure I have a card on file (I even added a second card). I can't seem get to a screen that will let me begin to set up an account for her (like give her birthdate, etc). Searched the online help to no avail. I sometimes get a message "can't access iCloud right now", too.

Is there something specific I need to do in the App Store to allow me to get out of this "do loop"?