Esc not arming but pixhawk does

Hello everyone, I’m trying to do a RC boat and for that i was trying to control the motor through the Pixhawk 2.4.8. The apm does the arming and it makes the respective noise but the esc is not ?
The receiver is connected to the RCIn and the esc is connected to the main output 3, afaik that is the throttel.
Did anyone stumble on this? I’ve deactivated the safety switch in parameters.
Thank you!

It sounds like you are using Ardupilot.