Hi, i'm using your mod on a server but i can't put the backpack on the armor. The piston boots works, the backpack not... why?

The backpack doesnt go into the armor slot.
To put the backpack on, right click with it in your hand and click on the button on the bottom left.

I do that but once I need it I can't get it off. What do I do?

press the b key to open up the backpack, then press the same button

Ohhh... Thanks!