Wife and I have the identical iPhone XR. Her's is "compatible" and mine is not. Why ?

I am trying to add my UNLOCKED VERIZON IPHONE XR to my Mobile account.  Says it is "NOT COMPATIBLE" yet my other IDENTICAL iPhone XR (also Verizon) is on the system with no problem.  The "not compatible" one has been on Verizon, T-Mobile and Total Wireless (Verizon MVNO) with no problem.  It was purchased from Verizon as was the other one.  XFINITY MOBILE SELLS IPHONE XR's so why is mine not compatible?  Makes ZERO sense.