Apparently the only way to the two way talk works via the mobile app is if you have a speaker connected to the audio out on the camera, and the microphone in on the camera. Both the speaker and the microphone need to be powered.
Otherwise using the twoway talk is only accomplished through the NVR using the audio in and out on the NVR (same rules apply). This is not advertised and painstakingly tested by me. Amcrest was no help whatsoever.