Help! GROHE Wall Hung Toilet Hanging

Hi all, I have been doing some diy plumbing and fitting a GROHE Wall Hung Toilet. I've got as far as fitting the pan to the fame but want to know how the seat pan fixings work before I build a false wall and can't get to them.

My question is do the seat fixing screws need a washer and nut the other side of the frame (See photos) or do the screws simply thread into the frame?

No mention of washer and nut in the instructions but without the screws move a lot more and doesn't seem as stable.

Any advice would be awesome, thanks!

You may need to adjust the position of the bolts to take into account the thickness of boarding and tiles. If you have locked them by putting nuts on the back, this may not be possible. Follow the manufacturers instructions.

Thank you for your response. I didn't have much faith in the setup so was looking for someone to confirm it.

I don't suppose you would know the limitations on the thickness of the wall between the frame and the seat pan?

I'm looking to fit 12mm plywood and then 12mm aqua board to create the false wall.