I am using a FlySky (which is NOT the same as FrSky) i10 Transmitter and iA6C receiver.  The receiver has both SBUS and PPM output.

After trying unsuccessfully for days to get the SBUS working, I decided that I needed to go back to PPM.  I connected the PPM output of my 
receiver to the "R" pad on my SpeedyBee f405V4 board.  I had it previously connected to the SBUS pad.

In the PORTS screen I turned the "SERIAL Rx" slider OFF.  Then I SAVED and rebooted.

In the RECEIVER tab, it said "Serial (via UART)".  I changed that to "PPM".  I SAVED and rebooted.

When I connect again, it still says "Serial (via UART)"  and refuses to change.  No matter how many times I set it to PPM,
it will not change.

What am I doing wrong?

I realize that PPM isn't as responsive as serial, but I couldn't get any serial mode to work. I just want to get this thing in the air.

the manual/diagrams from speedybee are excellent, should make setting up sbus pretty easy.. but ppm should also work. Which 'R' pad did you connect your receiver to? it will only work on R2, so if you hooked it up anywhere else, you won't get it working.

betaflight reverts to a previous state when you apply a configuration it doesnt see as working, so if youre setting to ppm and it changes itself back, it doesn't see ppm.

also, what version of betaflight are you running?

Are you running BF 4.4? If so you will need to select the radio protocol(s) you plan to use when you flash the firmware under Build Configuration. Otherwise you will not be able to select it.