DIAGNOSIS: F9 or F9 E0 indicates a communication error between the primary control board and the touchpad/display board.
FIX: Unplug the microwave for 5 full minutes to perform a hard reset. This can clear a temporary glitch. If the error returns, the flat ribbon cable connecting the two boards is the prime suspect. Reseat this cable by unplugging and firmly reconnecting it at both ends (control board and touchpad).
IF THAT DIDN'T WORK: One of the boards has likely failed. Moisture or grease ingress can corrupt the touchpad board. Given the cost, you'll need to diagnose which board is faulty, but the touchpad is the more common failure point.
HEADS UP: Before condemning the boards, ensure there's no visible moisture or obvious spill damage around the control panel. Spills are a frequent cause of this specific error.