I've downloaded the trainer and tried to use the option "unlimited ammo" but it doesn't seem to work. In the opening scene of the game, when I shoot my gun, the bullets deplete and eventually reach 0. Is there an issue with the unlimited option in the game.
No, there is no issue. The Unli Ammo option is working fine. You have to had bullets in your inventory in order to have Unli ammo. Just use the No reload option at the beginning then disable it and switch back to Unli ammo once you've picked some Ammos inside the RPD station.