How do I progress after listening to the audio?

It's 3164212.

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You have been sent an audio file in a conversation with Zac. Listen to it to hear some tapping sounds. This is a clue.

The tapping sounds will give you numbers. 3 taps followed by 1 tap etc.. this then will give you a phone number. Go to your phone and dial the number to get the next part of the game.

Check the guide at https://www.appgamer.com/an-elmwood-trail-walkthrough-guide/ for help