in primary sound device go to settings and enable stereo mix; if already an option select " stereo mix" as primary sound device. and select: 1- save audio tracks while recording; 2- "two sound mixing'. try and you'll get the PTT to work.
If we select Default for the first sound option then bandicam doesn't record videos it shows out put of two files one wav and one mp4 which have both duration of 00:00.