IMEI not compatible - Samsung S23 Ultra(International purchased)

I have a Samsung S23 Ultra which I had purchased internationally and wanted to port my number to Xfinity, but the Xfinity website and customer service says that the phone is not compatible. I am currently on Verizon Wireless and works perfectly fine. Could someone help add on this regard? Can an IMEI be added to the database so that it would be compatible.