How to create an iOS plugin that takes recordings from the mic and plays it back through the speaker (live)?

I'm trying to see if I can get the functionality of MicInput by Stefan Mayer-Popp onto a Unity game. What MicInput does is take the audio heard by the mic and output it to the headphones / speakers.

So far, what I've tried is to import AudioProcessor.m, AudioProcessor.h (renamed TestScript), and my own "extern" file that accesses Start and Stop functionality from said files.

While it does run without errors, all I'm hearing are rapid-firing clicking sounds, and per the comments, the function recordingCallback is not being called.

I'm not sure what is happening, so could anybody suggest a way to create a iOS plugin that does the above task?