Is this little tab suppose to be spring loaded?   Mine moves freely back and forth.

That tab lets the camera control the aperture on the lens, which should have a very similar tab. Really just a mechanical pass-thru needed as the teleconverter sits between the lens and camera.

So u don't think it's spring loaded?    I tried it on my D780 and it shoots fine.   Just got it from MPB today.

Thank you.   That's what mine does.

I don't think the tele-convertor should have a spring on that tab. The lens does have a spring, so when the tele-convertor is connected to the lens the tab is put into the correct position to attach to the camera. If both the lens and tele-convertor had springs then there would be twice the resistance when the camera tries to set the aperture, leading to more wear and possibly even not having enough force to overcome two springs instead of just one.

Always connect your teleconverter to the lens first. This will then use the spring in the lens to align it when you mount the whole thing to the camera boby. Thats how I always have done it and have never had an issue.