Android (child) cannot make a purchase since iPhone (parent) doesn’t have Google play and therefore cannot add payment method to this app

I have an iPhone while my child has an Android. We use Family Link.I want to approve an in-app purchase on his phone, and I understand that I need to add a payment method to my Google Play, but since I have iPhone I don’t have Google Play, and therefore, he is unable to make any purchase on his Android.

How can I solve this issue?