The mode's own start-up check said no

What ArduPilot says:

• init failed

Each mode checks a few things before it starts. Auto needs a mission (and, armed on the ground, one that begins with a take-off). RTL needs a home position. SmartRTL needs a recorded path. Flip must be entered in flight from Stabilize, Acro, AltHold or FlowHold, without the roll stick held hard over. AutoTune must be entered in flight from Stabilize, AltHold, Loiter or PosHold with the throttle off zero. FlowHold needs a healthy optical flow sensor. Throw and Turtle must be entered disarmed. Follow needs FOLL_ENABLE at 1, SystemID a test axis.

What to do, most likely first

1. RTL: home was never set, because the copter armed and took off without a position.

   CheckThe ground station shows no home on the map.

   FixWait for the position before arming. Home is set at arming when the position is good, or later, the first time it becomes good.

2. Auto: no mission is loaded, or it holds nothing but the home point.

   CheckMIS_TOTAL is 0 or 1.

   FixUpload the mission and read it back to see that it arrived. A message “Auto: Missing Takeoff Cmd” has its own explanation.

3. SmartRTL: no path was being recorded.

   CheckThe log has “SmartRTL deactivated”.

   FixSee “SmartRTL Unavailable”: the position was not good at arming, or the path memory filled up.

4. AutoTune or Flip: asked for on the ground, from a mode that does not allow it, or with the throttle at zero.

   FixTake off and hover first (AltHold is the usual choice for AutoTune), then move the switch.

5. Turtle: SERVO_DSHOT_ESC is 0, the copter is armed, or a stick is off centre.

   CheckRead SERVO_DSHOT_ESC: 0 means ArduPilot does not know the ESCs take DShot commands.

   FixTurtle reverses the motors with a DShot command. With DShot ESCs set SERVO_DSHOT_ESC to their type; then disarm, centre the sticks, throttle down, and select the mode.

Parameters to look at

Where to do it:Setup & Tuning GuideMission Energy Check