Cell service for new Apple Ulta 2watch, not supported by T-Mobile

I just bought a new Apple Ulta 2 watch from Best Buy. I tried to activate cell service through T-Mobile. I have cellular service for my iPhones from T-Mobile. T-Mobile tells me that my new Apple Ulta 2 watch is not supported by T-Mobile and that I should buy an “upgraded model” . I called Apple support and didn’t receive any help from them either.