I bought a Neewer NW564EX a while ago. I've used it on camera, and it works very well from the hotshoe. The specifications say it is compatible with Nikon cameras as an i-TTL slave. Recently, I tried testing it off-camera, and I can't get it to sync. I have the on board flash set to Commander Mode, and the flash set to i-TTL slave on group A, channel 1.
When I take a shot, I can see the flash fire, but it's not very bright, and contributes nothing to the image, which remains heavily underexposed. I have been able to use the flash as a manual slave, fired from the on-camera flash in manual mode, but I'd prefer i-TTL functionality.
I'm hoping it's just that I've missed something in my settings. I've uploaded images of the camera and flash settings for review.