Problem setting G-sync on Dell S2716DG

[CaptainBlack]

Hi all. For the life of me, I can't seem to set up G-sync.
I have set my resolution to 2560 x 1440, refresh rate 144Hz.
Enabled G-sync full-screen mode in G-sync setup.
I only have the one monitor connected in Multiple displays and it is selected.
But in "Manage 3D settings" when I click on Vertical sync it only has:
Use 3D application setting.
ON
Off
Fast
No G-sync setting? What am I missing?
It is connected via the supplied Display port Cable.
My rig:
GPU-Asus GTX 1070 Strix
CPU-i7
MB-MSI Gaming Pro Carbon
RAM-16Gb
Storage-Samsung Evo 500Gb SSD

 

[CaptainBlack]

G-Sync is enabled - the V-Sync entry in Manage 3D Settings now controls how G-Sync works - Off runs uncapped with G-Sync applied upto 144Hz and disabled if you can render above 144, On has G-Sync always enabled and capped at 144Hz/FPS and Fast renders as fast as possible but only renders frames when they won't tear.

Many thanks Rroff.
I followed 3 guides posted online and they all showed a G-sync option in the V-sync setting!
What setting would you recommend I go with for daily gaming?