Transfer Existing Xfinity Mobile #

I have been trying to transfer my existing # that I have with xfinity mobile from my iPhone 13 Pro Max to my iPhone 14 pro Max but I keep getting an error message saying the following “Your sim is not supported. This phone number can’t be transferred because the number is not allowed by your carrier. Contact your carrier to unlock this device. Well Xfinity Mobile is my carrier I’ve been a customer with you guys for 6yrs. Why is this process so hard to complete ?