Dot and dabbing adhesive for foam core backerboad

You need plasterboard adhesive and they need to be dotted every 300mm (12") and then mechanically fixed with drilled, plugged screws - For Aquapanel or similar cement-board.

If it's Marmox-type foam board with blue foam in it. Then you'll need to spread tile adhesive that's flexible (S2 in UK I THINK) as if you're tiling the boards to the wall. As this will give you protection against the weight. Don't dot and dab those types of boards. They're mean to be spread, on the wall, then stuck to that as if a big tile.

You can spot bond but only with boards that are 20mm or thicker and then fix through the dabs. You can use tile adhesive but not thicker than recommended depth. Otherwise as above you need to fully fix.