Check limits message and help seetting up the 3018 PROver laser

[Saxophone27]

I am a complete beginner to the laser function of the 3018 PROver and am really struggling to set it up. I keep getting the "check limits" message up even though I'm sure I've set this up correctly. I also cant see the laser beam for the 5.5 blue fixed laser. If I press in the fire button it stays on and sets the laser going - but I cant see anything when I press the button for laser on lowest for 2 seconds.
Does anyone have the complete GRBL code setting for this at all and any advice on how to set the limits? Thanks In advance!! :)