may not work on all items. Some items you have to use the other option
NumPad5: Unlimited Heavy Weapon Ammo
otherwise some weapons it may not work at all.
Well F me, today I fired up OBS to make a video, started the trainer, started the game, activated the trainer, went into an offline game, used Numpad 1, 3, 4 and 5 and it worked on the Mk110... I did the exact same thing yesterday, but it didn't work with the Mk110. Same trainer, same game, same computer. I love these kind of shenanigans...
To me it seems you did use the trainer incorrectly, because it works fine for me.
Did you run the trainer as administrator?