> but in Android, Autoplay works...this issue is only for iOS devices
Yes, InstaVR did our best to avoid this autoplay limitation on web browser. That's why audio and video are autoplayed on Android.
Actually, the workaround worked before iOS 11.x. Apple introduced much strict policy to web browser so previous work around didn't work anymore.
Google is going to apply restriction for mobile web browser's autoplay recent, so audio and video might not be autoplayed on Android in the future.
Updated: Google add restriction for autoplay at Jan, 2018
Google: Autoplay Policy Changes