Could be igniter, or sail switch. Also you may be low on propane. Three attempts at ignition is typical and then shut down.
The circuit board has a green ground wire that is held to the frame with a sheet metal screw. Find that wire, remove the screw, brush the surfaces of the crimp connector and the sheet metal where it is touching then re-install the screw and verify it is tight. While you are at it, remove the push on electrical connector on the circuit board, clean the board connections with a pencil eraser. Put it all back together and hope.