I've used this set up successfully before, but now I can't figure out what the problem is.
I have the YN622N-TX in the D750's hot shoe, and the YN622Nconnected to the YN568EX flash off-camera. When I press the test button on the TX, the flash fires, so the connection from there on is fine. The shutter does not trigger the flash though.
If the flash is attached to the hot-shoe, it does fire. The flash has the icon for on-camera flash showing, and pressing the mode button for a long time, as described in the manual, doesn't switch it to off-camera mode (or do anything at all). I don't remember having to manually switch it in the past.
Is there something wrong with the flash unit, if it's not switching, or am I doing something wrong?