I did a online chat with Asus service.
They told me that M.2 PCI-e 3.0 X4 is compatible and AHCI and NVMe are both compatible (Say's the documentation of the laptop)
Also you need to buy a SSD which is NGFF 2280 (the left one on my picture)
But I'm still wondering what is really compatible and working.
And what type of connector is needed? I suspect the right one?
Perhaps you can check which SSD is in your laptop?
ACER PREDATOR G9-791 |Intel Core i7-6700HQ |16 GB RAM |GTX970M 3GB |FULL HD | 750GB SSD | Samsung 850 PRO & 2X M.2 SSD RAID 0
G75VW |Intel Core I7-3610QM |24GB RAM |GTX670M 3 GB |FULL HD | 526GB SSD | Samsung 840 EVO & 850 PRO
GL552VW |Intel Core i7-6700HQ |12 GB RAM |GTX960M 3GB |FULL HD | 256GB SSD | Samsung