On Clicking a button enter VR Mode, element.requestFullscreen() is executed by calling the function requestPresent([{ source: _this.m_renderer.domElement }]);

requestFullscreen throws the error Failed to execute 'requestFullscreen' on 'Element': API can only be initiated by a user gesture.

So entering full screen is failing followed by below errors:

Uncaught (in promise) TypeError: fullscreen error
at requestFullscreen
at new Promise ()
at CardboardVRDisplay.VRDisplay.requestPresent
at HTMLButtonElement.button.onclick

Same error appears on mobile while visiting https://immersive-web.github.io/webvr-polyfill/examples/ and on clicking the VR button.