I bought the watch and tried setting up mobile data on her watch from my own carrier. It said it is not supported. Fair enough, I went and bought her her own number, installed as an eSIM on my phone. Same result - will not let me setup mobile data. I went to my network provider and explained them the situation. It took a long time to explain why I have 2 watches on the same phone. Some of their staff said it is not supported. I took time to explain to them how family setup works and showed them Apple’s article saying it is supported for this carrier. They called people internally, spent a lot of time, but no one had heard of this or knew how to activate this.
So I went to another carrier here (also on the list on Apple’s website) and explained the situation to them and asked them if I bought a connection from them whether it would work. Same- no clue what I meant/wanted.
I have no idea what to do now. Should I just return the watch and give up?