I set my watch up for family member so I can have cell service. I did this because I use my work phone as my personal phone and it has a different carrier. My problem now that I have it set up this way that watch is almost worthless. I have cell service but can’t download apps because it requires a credit card which I can’t add. WTF! They should have just made a toddler version instead. Why put so many limits on stand alone sevice?
The family paired Watch should be set up with an Apple account specifically for that Watch user and on setup you should have been able to add a credit card. It would be a different account from the "parental" iPhone irrespective of who the actual people are.
Bear in mind this is set up for kids so don't be surprised at the restrictions and unavailable features described in the article Set up Apple Watch for a family member - Apple Support but that would not restrict credit card or app purchases.
Apple Watch
