If it doesn't ignite at all its likely:
- Low propane pressure. Even though it will light with a lighter it may not have correct propane pressures and may be insufficient to light from spark. Not likely but possible.
- Weak spark. Since you indicated it is sparking, it could still be too weak to ignite. This could be caused by mis-adjusted igniter, bad igniter, or bad control board.
There are a number of other possibilities but most of them would result in the flame igniting but not staying lit.
Here is a link to a troubleshooting guide I found with a google search. I'm in no way affiliated with this web site, just found the guide has helpful troubleshooting information...
2018 Forrest River Salem Hemisphere 282RK - 2017 RAM 1500 TV
Previous RVs and TOADS
2004 Fleetwood Bounder 32W on WH W20
2000 Four Winds 5000 21RB
1986 27' Allegro
TOADS
2005 Ford Ranger XLT 2WD
2004 Suzuki Aerio
1988 Chevrolet Sprint