The motor interlock switch is in the way

What ArduPilot says:

• PreArm: Interlock/E-Stop Conflict
• PreArm: Motor Interlock Enabled

A switch with the function Motor Interlock (RCn_OPTION 32) lets the motors run when it is high and holds them stopped when it is low. “Motor Interlock Enabled” means it is high or in the middle while you arm: the motors would start at once. “Interlock/E-Stop Conflict” means a Motor Interlock switch and an emergency stop switch (RCn_OPTION 31 or 165) are both set up, and the two cannot be used together.

What to do, most likely first

1. The interlock switch is not in its low position.

   FixMove it low, arm, then move it high when you are ready for the motors to spin.

2. Two motor-stopping functions are assigned at once.

   CheckList every RCn_OPTION and look for 32 together with 31 or 165.

   FixKeep one of the two and set the other channel's RCn_OPTION to 0.

Parameters to look at

Where to do it:Setup & Tuning Guide