Why audio doesn't work when browser initializes the video call

I'm developing a WebRTC app. It's supposed to be used for video calls between a mobile app and a web app.

When the call is initialized from mobile everything works perfect. But when the web app initializes the call there is no audio. Video plays normally in both situations.

I'm using this code for audio permission

navigator.mediaDevices.getUserMedia({
  audio: false,
  video: true
})
  .then(gotStream)
  .catch(function(e) {
  alert('getUserMedia() error: ' + e.name);
});

Is something wrong with the code or is it some WebRTC specific issue?