Use Apple watch on my iPhone on another account cell plan

My friend is on T-Mobile. I’m on T-Mobile but on my own account. Two separate T-Mobile accounts.

he bought an Apple Watch SE through this T-Mobile account with a standalone plane.

he gave me the watches as a gift. He’s going to make the cell plan payments.

I tried to set the phone up with my iPhone and it can’t find a cell plan. I don’t see anyway to tell it to use the cell plan on his account but pair to my phone.

he set it up ‘family’ so it’s working but only on his phone. My phone can’t see it obviously.

All he’s trying to do is buy me a gift and pay the monthly payments.

is there anyway I can pair to my phone yet use the cell plan on his account.