Guys I have a problem withthe mx-20

I'm using it for a mikrokopter, my receiver is the GR-32 (4 antennas), and the connection to the mikrokopter is via SUM channel (single cable).

I set the failsafe as described in the manual, selecting POS (position) for all channels, then I press SET and I get the message "Position Stored". But nothing happens if I turn off the radio. What is the problem ?

Thanks