Unable to bonus pot secondary weapon

Describe the problem. Be as specific as possible!:
I am unable to put bonus potential on my Feather (BM secondary weapon. I tried using both Special Slot Carver 100% and the normal 60% bonus pot stamp.

 Images of problem

It just says, "Cannot be used on this item". When I try to place it there.

Does this happen for all new secondary weapons?

I used a special bonus pot scroll on mine. Using legendary spirit? It's bugged.

I tried to bonus pot my lv100 KoC secondary with the 10% stamp, didn't work.

Dont use legendary spirit.

those carver slot potential doesnt work on item that has no bonus potential cuz it either bug or they are design that way