Apple Watch SE / Family Sharing / App Store Issue

Apple watch SE - when I try to install apps on watch (for family shared child's watch) it says "Unable to purchase app, sign in with your apple id from the apple watch app on your iphone". There isn't a place in the watch app on my iphone to do so.

I have the latest ios 14.0.1 on my iphone.

Keep in mind - this is my 11 years old son's watch that with Family Sharing, is standalone, and he doesn't have his own iphone. This is a new feature with watch 7.0.0. It's managed from MY iphone, but has it's own cellular number and HIS apple id account.

Thanks for your help!