I'm hoping someone else has run into this problem and perhaps has a solution. I purchased my daughter an Apple Watch SE. She does not have an iPhone and it is currently configured under the family setup. We went to the T-Mobile store and they set the line as "Mobile Internet" and entered in the EID. When we attempt to enable Cellular on the watch we receive the following error "It looks like the watch was set up with a incompatible plan." I have now spoken to FOUR T-Mobile reps who all insist the device is set up properly. They now have a ticket opening with their engineering team, but after hours wasted I'm not feeling confident. I've received 9 texts so far this evening confirming that my line has been paired. I'm not even certain if the mobile internet line NEEDS to be paired with my own line to work?! I would love to hear any feedback T-Mobile users may have. I am on a "T-Mobile ONE All In" plan if that makes any difference.