I have the Pi-3 and there isn't a MIC input on the Pi itself.? Unless you have an external sound dongle you are using there will not be an RX device.
These USB Sound dongles are like 5 bux on Amazon (make sure linux compatible.)? Running the command aplay -l && arecord -l? will tell you the devices available?for record and playback.? I ran in to this with Direwolf.? The PI can send out via the 3.5mm plug but there is no input.??