I traveled to India in 2017 and 2018. I had problems getting HSPA+ most of the time. Had no problems with local carriers.
Last night on the way to some mall we took a route though some sort of jungle dairy farm. Both of the locals had no signal when about half way through traffic stopped ( except for the masses of motor bikes, they just keep comming ). I was the only one able to pull it Google maps and check how far up thr road the traffic was.
Maybe Mumbai is set up better for Fi? What parts were you in ?
Also. The main post here should be about Google payments, not Fi.