DIAGNOSIS This is almost certainly the low oil shutdown doing its job. The XP12000EH has a sensor that kills the engine if the oil level gets too low, and it won't restart until you refill and manually reset it.
FIX First, check and top up the oil to the full mark on the dipstick. Then, you need to reset the low oil alarm. Look for a red rocker switch or button on the control panel near the start switch labeled "Low Oil Alarm Reset" or something similar. Press and hold that reset button for a few seconds. Now try starting it normally.
IF THAT DIDN'T WORK If it still won't crank, the sensor itself might have failed in a "safe" state. You'll need to locate the low oil sensor (on the side of the engine crankcase, with a single wire connector), unplug it, and try starting. If it starts with the sensor disconnected, the sensor is faulty and needs replacing.
HEADS UP This shutdown can happen faster than you'd think on a new engine during break-in, as it burns a bit more oil. Always check oil level before every use for the first 20-30 hours.