I compared your picture to mine and I think you have discovered the issue. I was on the wrong end of the adapter in my previous reply. Sorry about that.

In your picture, directly above the black thing the adapter is laying on and directly underneath the tiny screw in the picture, there is small tiny piece of shiny metal sticking out and "pointing" at about 4-O-Clock (if we were looking down on a face clock). Directly above the tiny screw is a rectangular cutout were the dark slide metal piece pushes in. Mine has a piece sticking out with the dark slide pulled. You can compare my picture1 with yours.

On my adapter, with the dark slide pulled out, I can see a tiny piece of metal that pops out (Arrow A in pic 1).

In Pic 2 I rolled the adapter out of the way so you can clearly see that piece A is pushed by the dark slide and rotate piece at arrow B out of the way and allow pin C to be pushed by the camera pin. I think...

These pieces are also in place to prevent you from taking the back off with out the dark slide in place.

Any way, if they do not take care of it, it may be possible to take the thing apart and at least see what the problem is, broken piece, stuck piece, broken spring, ect.

Good luck.