The aircraft does not have sufficient flight or cabin crew assigned.
are pilots and cabin crew assinged to this aircraft?
The aircraft was not located at the departure airport.
If you flight starts at point A and your plane ist still at point B or isn’t transferred to the starting point, Assign a transfer flight in the flight planner
The aircraft requires technical maintenance.
did you hire a maintanance company ? Is the maintanance rate of this plane 100 % or higher (but not more than 200 %). Is the maintanance condition of this plane "green" or at least "yellow"?