Have you considered starting a payments bank in another country where you can prove your idea with less capital? Then you can use the capital from that to get started in India or if there's not enough, you can use the experience to inspire investments to get the capital.
Also, I hope you're ready for an immense amount of red tape.
I have had the idea of looking at other countries before but I haven't put in time to figure out what countries I should be looking at. Will look into this.
Also, I hope you're ready for an immense amount of red tape.