Unable to add my daughter to Family Sharing

I was able to add my son to family sharing and signed into his new IPad but now it will not allow me to add my daughter to family sharing. Extremely frustrating. I currently only have myself and my son on family sharing.

it will allow me to do all the prompts and agree to terms but when I get to the final screen, a pop up comes onto the screen saying “your account cannot be added at this time.”

I’ve restarted all devices. I don’t know what else to do.

Please help!

[Re-Titled by Moderator]