Does the igniter work? Check it with an ohm meter. If it reads 0 or infinity, it's bad. Replace it. If the orifice is clean & not clogged, AND the gas is turned on, then it's the gas valve relay on the circuit board. Replace the board.

Is this furnace in an RV? If so, remove the gas orifice and clean it out. Probably a very small piece of rust or scale in it.

It won't ignite if it's not getting a good draft signal.

so what would be the problem exactly?