family link and whatsapp backup issue

hope you all could help me on this issue.
i have family link control over my 8-year-old daughter.
now, we bought her a new android phone.
the phone is under her own account we created on google.
no we had installed Whatsapp. but when we go to backup options in Whatsapp trying to backup the Whatsapp data to her google account, Whatsapp comes up with a comment that this can not be done. i suspect it is due to family link.
after approving all apps for her with zero limitations, still, i can not back up Whatsapp data to her google account.
do you guys know how to solve such an issue?