I can't cheat although I have played through the entire story at GTA v but not all side missions I'm looking forward to answers LG Gustav
Maybe because cheating is not an official GTA feature?
If you mean the standard cheats that are entered with a key combination, they are available from the start. You just have to know the combinations.
I know one of them:
D-pad right, A, D-pad right, D-pad left, D-pad right, RB, D-pad right, D-pad left, A, Y.
This cheat activates immortality for five minutes. Of course there are more cheats, you can find them on forums as a list, or in tutorials on Youtube.
But if you mean cheats that appear in the form of a menu in the game, this is not a cheat, but a mod menu. These only work if you have a modded Xbox 360 console. Such are hardware technically modified, and can bring enormous advantages to several games. However, the use of such modded Xbox 360 consoles is prohibited, something like this can lead to your Xbox account being blocked.
