How to fly quadcopter using APM 2.8 and Flysky FS-i6


I’m new to this and have trouble to control the motor using Flysky FS-i6. The controller that I use is APM 2.8.
I tested the compass motor calibration on APM Planner and it works well.
I tested the radio calibration it also works well.
What makes me consfused is how to start the drone to fly. I have followed some other
article that shows how to getting started with APM 2.8 drone and it’s not working. I also
tried to do some setups on the remote control or transmitter, and after turning off and on the drone, I can’t control the drone with the transmitter.
The arming indicator works well, but it seems like the flight controller can’t translate the
radio control input to motor pwm output.
The main goal is just to get the drone to fly, but I don’t really understand what is missing. I have tried several setups since last week but nothing can help me to fly the drone.

So, does anyone has any idea what happen? Thank you