Data with Paired Digits - Linking two CELL PHONE (NOT A WATCH)

I have been trying (unsuccessfully) to link two cell phones under what I believe is called the Data with Paired Digits plan. Tmo associates have been friendly but completely unable to get this done. It took awhile just to convince some of them that this was a service they offer -- even though right on their website. I am trying to use same phone number on two phones and want to use a second sim -- and not just app and internet to accomplish this. These are two different things -- also hard to find someone at Tmo that understand this distinction. At this point I am almost ready to throw in the towel. Does anyone really understand how this is supposed to work?

At this point two lines are somewhat synced. Calls register on phone devices. Texts aren't being mirrored on both devices. I am using pretty modern two android phones with recent android versions. I am using google messages app I have tried turning off RCS on both (which I would rather not do) but that didn't resolve anyway. Anyone know if it is really possible to have a mirror phone that work using this "service"?