I'm a newbie to Domoticz, so please bear with me

I installed DOMOTICZ on a raspberry pi 2 I had left unused.
I plugged a RFXCOMXL on a usb slot.
I manually added a switch with
Hardware : RFXCOMXL,
Name : DOORLIGTH,
Switch type : Dimmer,
Type : AC,
ID : I didn’t change it since it’s the first thing I do on DOMOTICZ
Then I pressed TEST… but nothing happened !
And I tried and tried, I moved the rpi closer to the switch… nothing worked !
HELP !
Thanks for your help.