If what i understadn you are trying to nuge the box manually, but this is not the case by pressing Player 1 E or Player 2 Alt you interact with the box picking it up, This is indicated by the glow around the box when you get close, Hope this helps unless i misuderstood your post! :DD
Oh, I see now. yeah, I didn't notice you can pick them up, thanks for explaining. Maybe change the level of the box shows the first time, so that you HAVE to pick up the box instead of just nudge it to pass the level, so player would try to find out themselves. Still, sometimes the nudge does not work when the character next to the box.
Yea the nuging was relly just a side effect of the kinematic body and wasnt originally even intedet to be a feature since you are meant pick up the box to move it but i kept it in to make the box feel more life like and have you be able to nuge it a little for more accuracy, but i guess i didnt make it rlly clear enought that you need to pick it up, hope you still enjoyed the game tho!