I've reported this before, but you can no put dirt in a container that's in a container (inside a bin in a cart).
So you either have to put the bin on your back and put the dirt in the bin then the bin back in the cart, or drop the bin, put the dirt in it and then pick up the bin and put it in a cart. (replace "cart" with building container if using that).
I believe it's a bug but still never been changed so now maybe just a feature . I believe it was before due to planned weight options but never got changed.