LineLink doesn't work with T-Mobile 5G home internet router

Update: As a test I was able to connect the LineLink to my computer and share my internet connection to it that way, and connect the computer to my phone's wifi hotspot, and that DID work.  So that rules out any problem with the SIM card.  But it still doesn't work when connected to my T-mobile home internet router, which is what I really need.

That said, I spoke to another T-mobile support person, and got a little more definitive information.  They said that there is a known incompatibility between the LineLink and the 5G home internet router devices.  Further, that this was not going to be fixed any time soon, and they recommended that I port my LineLink number to another provider.

I still think it's got to be something simple like needing to open up a port on the router or something, but from the sound of it, this won't be looked into for a while.  Perhaps weeks, he said.  Therefore I'm going to switch back to Vonage (which is what I was on before). 

I also just want to state, for the record, that the T-mobile support folks have been excellent and very helpful.  I believe the problem that I had being bounced around between departments is a systematic problem between their 3rd party support company and their main support, specifically with documentation and training perhaps, and just being overloaded and not being able to handle the capacity.  But the people themselves are great, both with the main support folks and the 3rd party support company.  They are doing the best they can.