Hello!
First off, I wanted to thank the dedicated developers for the work they’ve put into this. I’ve only recently discovered this emulator. SO AMAZING!
But unfortunately I have ran into a problem, for some reason I can’t activate cheats into the game. I’ve searched the net for solutions, checked mednafen forums as well, didn’t find anything because from what I understood the fork the devs are using is their own, not the one exactly from the devs from mednafen since they use cli and have their own front-end GUI. I can download the list from the github repos from the in-app menu, and can load them up when a game is running, but they don’t activate at all, even when I applied the changes to the activated cheats. I have tried using the current stable and the 1.2.2 build of the emulator, same thing. Haven’t seen anyone have this particular problem so this might be specific to me only. It might be because of the different version/region of the game?
Then can anyone tell me what region are the cheats for MGS1 are in the github repo? I tried the v1 and the v1.1 same results. Also the same with Dino Crisis 2?
A workaround I saw on the forums is to use GameShark, haven’t tried it yet, but if it works it’s quite a hassle to do. I’d have to input the codes myself (not that I don’t mind) 
I’ll also try with Crash Bandicoot: Warped later with cheats, will update you guys how it works out.
EDIT:
Tried Crash 3, didn’t work as well. GameShark worked though. Still, it would be nice if you guys can fix this. I looked around the net and saw that it might actually be specific to PSX only. I saw 2 people had the same problem. Problem with GameShark is that you can’t load your previous saves. Kind of a bummer.