Hmmm! I had to searched up and read up on "APN settings". I had absolutely no idea prior to this. I looked up in my iOS Preferences, could don't find them and honestly I don't want to touch those.
I am not sure what it is called on iOS but on Android it's called "Access point names". In that there are bunch of access points basically for data, mms. For Airtel you have to go into settings of "airtelgprs.com" APN and change bearer from IPv4 to IPv6 or IPv4/IPv6.
