Sonoff RF R3 Remote Receiver GPIO pin and config

Actually the question itself is in the title.
What pin is responsible for receiving commands in Sonoff RF R3?
I tried GPIO4, 5 (inverted and not) - no results.

Is the Answer in this list?

No, there is only sonoff rf, but I need RF R3. there is a completely different board. And for the old version there is no information on the receiver pin