Motor interlock issue

Hello to all of you!
kindly request your help in my problem, which after so many search and readings …unfortunately i can’t found any solution!!!
The point is that i’m very new to APM and PIXHAWK controllers and because of that, most probably, its something simple, but personally i’m totally stuck. So i please to anyone of you for your efforts!
So, to start with firstly to tell you my setup. I use a 450 class electrical Heli, and Pixhawk fmu controller. I use Futaba Tx T8FG super and Rx Futaba R6208SB Mission planner 1.3.49 version and Helicopter firmware 3.5.3. Everything went well with the main setup (servos moves correctly, and the Green bars in mission planner also well).
The controller after powering it on, gives me Green flashing light. BUT whatever i try i CAN’T (in any way) ARM my motor!!! It gives me all the time the message “Prearm: Motor interlock enabled” Which really i don’t have any idea how to get rid. I try sooooo many thinks and i spent soooo much time for it …but without Success.
Please Help me to solve it so to be possible to arm my Heli!
Any help will be MUCH appreciated.
Many Thanks in advance …Dim

Motor Interlock (32) is an option for Channels 7 thru 12
Check with the parameter documentation here

Thanks for your response, but unfortunately this advise from you, didn’t helped me. As I say I’m very new to these controllers, and searching in parameters, doesn’t say anything to me (at my present knowledge state)
By the way, after lots of reading, I assign in my tx a switch which corporate with ch8 in mission planner. Also I play with end points for ch8 and when this switch is ON it gives 985 minimum value!!! Like this the error message disappeared, the green led on the controller is flashing green BUT surprised me because stil (without a warning any more) I can’t arm my heli!!! Really strange, probably I miss something more!!!
In any case …once again Thanks for your response.
Be well