Nikon Flash Pass Through on Sony A7Riii?

Teddy

I have a Nikon SB-800 flash and a Sony A7riii. I also have a Cactus V6iiS. 

I want to use my Nikon SB-800 flash mounted on the Sony A7riii camera. I stack the flash on the V6iis, then put it in the camera hotshoe.

I cannot get the flash to trigger with this setup. 

1. Is it compatible? 

2. Can I use HSS and TTL?

Thank you

lansa301

@Teddy
I am sorry, but that setting is not going to work.
The V6IIS have the SONY MI (Multi-Interface) proprietary hot shoe on both sides, male on the bottom and female on the upper.
The MI hot shoe looks very similar to the iISO hot shoe but have all contacts on the front side, not on the shoe bottom.
I am not sure if you can find a hot shoe converter from Nikon TTL to SONY MI.
My
advise is, find a nice flash bracket and use your flash off-camera. Not
only the flash is better positioned to get more pleasant light but is
more balanced and comfortable to use it on that way.
And you will have all advanced features available with the V6IIS (HSS, TTL and many others).
Regards,

Antonio

Yeah, as @lansa301 mentioned above, what you wanted to achieve is currently not possible. 

Due to the uniquely designed hot shoe by Sony (as usual), you can only mount a Sony system flash as on-camera.

@Teddy perhaps you should consider getting a Sony flash and use your Nikon for off-camera.

Thanks!