Transmitter not calibrating

I have a FlySky FS-I6 transmitter I am using for my Hexacopter with a 2.4.8 Pixhawk autopilot. I go to do the calibration in mission planner, and nothing shows up at all. What would cause this, and how do I fix it?

check your cabling and power. other than that ive got no idea

Hope you have switched ON PPM Output
in the transmitter