I called Xfinity support today for a PUK code and after some time with "Tech Support", I was told that I had to take my phone to an Apple store to unlock my iPone 8. This is unacceptable in that the PUK code is a carrier issue.
Does Xfinity have access to this code? No it wasn't printed on the card the sim came with either!!
A PUK (Personal Unblocking Key) is different than unlocking. A PUK code is needed when you enter your SIM card PIN number incorrectly three times in a row. The default PIN is reportedly 1111. If Xfinity Mobile is not able to find a PUK code for you, you may have to get a new SIM card.
If you are trying to get your iPhone 8 unlocked in order to use other provider SIM cards, it must be payed off and you have to follow the rest of the Xfinity requirements. https://www.xfinity.com/support/articles/unlock-mobile-device