I can testify to this, bought from apple. Had lots of issues trying to
connect with o2. Hours of time with o2 support later and still not
resolved. I would stay away
I have the same problem, upgraded to new Apple Watch. Attached the
mobile data but says no connection. I called O2 and they are issuing a
new eSIM. Have to wait for it to be sent out. Hopefully that will solve
it!