Installing plywood onto chipboard floor

[JJayy]

I am preparing to install TLC True Forest vinyl planks. I had been planning on putting it straight onto the 22mm T and G flooring grade chipboard we have over the underfloor heating (as the chipboard is new, clean, does not have any gaps and does not seem to have any movement).
But following advice I will put plywood down first. What is best to fasten it down to the chipboard? Eg a 20mm screw, and then fill in the countersunk heads? What's best to use for this?
Ay further tips appreciated! Many thanks.

 

[dazlight]

Use ring nails mate.
20mm.
Nail every 6 inches all over and every 4 inches on perimeter of each sheet of ply.
What adhesive did you get for the tlc ?

 

[JJayy]

Thanks. I got F44 adhesive.