How to differentiate between auto call answer ivr and real audio of human

You can check what applications are available by going to the Asterisk CLI: asterisk -r

Then core show applications.

You can get more details on each one with core show application _____ (fill in the blank)

Something (ok, several things) seems weird about what you are saying.

Really? Then how…

FreePBX 15, webrtc, …?

I will assume that these are different customers you are working for.