Unfortunately I don't have that Tx/Rx to do testing of my own. Hopefully there is someone in here that has that combo and can help out.
One thing to check, when you choose PPM or whatever, make sure in the ports tab that it is still showing the port open that you want to use. And also do a google search for "Fly Sky IA6 CC3D Betaflight Setup" and it may point you in the right direction. I do wish I could have been more help on this, I just have never tested with any of these kinds of Tx's before.