Xfinity is usually code 1014 in Flipper V6 and 3084 in Flipper V7 and above (version is on the back).
But Xfinity is usually installed in RF (radio frequency). Flipper is an IR (infra red) remote.
So we need to activate IR in the Xfinity. They have different boxes, so you may need to contact Xfinity to determine how to activate IR on your specific box, but try: Menu>Settings>Remote Control>Activate IR.
Other boxes require a set up code. We think the instructions are: press and hold Setup button until light solid, then enter 987. But check with Xfinity for this code.
Then set up Flipper as normal:
1) set TV;
2) set STB;
3) Dual Mode: press and release ADD once;
4) Lock: press and hold ADD until light solid, then enter 955.