When you’re connected to Mission Planner (and battery) do you see the battery voltage there? Yaapu will mirror whatever voltage is displayed on Mission Planner.
https://ardupilot.org/copter/docs/common-powermodule-landingpage.html
No I don’t see the battery voltage.
edit: the other PX4 3DR installed in my other bird not working.
I think becasue its an old unit.
I have to find better newer unit to replace this one.
Thank you
My bad, I forget to answer your question,
It’s this one
https://www.getfpv.com/betafpv-elrs-2-4ghz-micro-tx-module-1w.html
So far no issues and the signal is good 
Thanks