I recently started using Verizon Fios TV service. It is a big difference from the Comcast Xfinity X1 platform. That aside, I was having trouble getting the 'A/V TV Input' button on the P265 remote to work with my Vizio TV. The simple instructions on the back of the remote would get most of the buttons working: power, volume, mute, etc. The 'A/V TV Input' button did not respond. If I wanted to switch to another device, I would have to use the button on the side of the TV. I will note I did not have this issue with the Comcast remote even using the simple setup instructions.
I searched Google and did not find any answers that worked. So I took a step back and followed a simple user perspective: I went to the Verizon Support page. I searched for 'program remote' and found instructions for programming the remote. Simple enough. First step was to locate the remote control code for the TV. The code for a Vizio TV using the P265 remote is 424. I followed the instructions and it worked! I could now switch input on my Vizio TV.
TL;DR - Follow instructions here and use code 424 for P265 remote for a Vizio TV.