When pairing the 20S to a non-Sena bluetooth intercom, such as the Interphone, the manual omits to mention that when both devices are waiting in pairing mode, to push the Phone button on the 20S !
Wasted an entire day trying to pair my 20S to my old Interphone F4 ! ! ! ! ! ! ! ! ! !
I hope this saves someone else the same utter frustration that I went through. I was about to take a three-pound hammer to this 20S.