Ok so I put back in the sim that came with the phone and then activated it online and now it only shows 4G. Can anyone help.
Put back in the iphone the 5G sim (R15). Then call and say that you need to activate 5G sim card.
They will ask for the 15 digit sim#. Read it off the iphone box - ICCID#
Then they will deactivate your 4G sim and activate the 5G
You can also message them in the tmo app which I find faster than a call.