Cannot start L-39 Albatros

Not sure what’s going on here, but when I follow the checklist, the engine for the L-39 Albatros does not start. I’ll turn on the battery, move the red lever forward, and hold the starter for 2 seconds. Then when the turbine light pops on and I hit the APU starter for 2 seconds, the RPM will rise, but the engine doesn’t actually start.