I was having the same problem you were having. Finally figured out the problem. The newest version of Vitacheat is only compatible with 3.65. The way around this is to use version z04 of vitacheat.skprx. I can't find an "official" download as the plugin's github only seems to host the newest version. But I found a download link on /watch?v=GHPgZg-eyKg [Youtube video ID] (can't post links because I made this profile just to post this comment) and used that skprx along with the files retrieved from autoplugin and got it to work.
So the order of steps, if that didn't make sense:
- Download autoplugin, and use it to install vitacheat
- Download the vitacheat.skprx from the video linked above (I'm only using the skprx because the other files may be out of date)
- Transfer the downloaded vitacheat.skprx to your vita and overwrite the one downloaded by autoplugin (autoplugin defaults the install to ur0:tai for me)
- ...
- Profit
autoplugin should take care of editing the config.txt for you so you shouldn't need to worry about that. Just reboot your vita after replacing the file.