I went ahead and started pulling screws, which was a real ---smurfette---, from the reject button assembly. The screws on the back of this thing are awful...two have a phillips head, and two don't. The two that don't have a socket type head but it's tiny...no socket I have ever seen would fit those. I had to use pliers to turn them and get them out.
After I got that assembly off, I found that there was a plastic piece blocking the coin slot. I did some searching and it looks like this piece is what goes on the dummy doors when people order Happ coin doors without the mechs (when using the door for cosmetics only).
I pulled these pieces out and everything seems to function fine, the coin goes into the slot and comes out of the mech at the bottom.
Jason