Here's the end game: a payment/retail aggregator app like Flipkart's Phonepe could buy out your business and integrate it with theirs. Acquisition would be faster than building a stock trading service internally. Paytm, their competitor, already got approval to build a stock trading platform. Diversified financial offerings cement first mover advantage and create a very profitable position in an oligopoly.
In the U.S., this space is marginally less exciting because there are multiple stock brokers with good or good enough tech platforms, reliable service, and hundreds of billions of dollars under management.
A bit of advice on the product itself.
1. Try to integrate with other Indian fintech platforms early on.
2. Learn from Chinese fintech. They created a model that can be more or less copied throughout the developing world. For example: Ant Financial followed the principles of choice architecture to save Chinese savers from making ill advised investments. They deliberately put safer as opposed to riskier stocks on their stock trading platform. They knew that even Chinese people didn't trust Chinese stocks a lot anyway, so they leaned on global offerings and partnered with Vanguard to encourage investment in diversified foreign indices. Ant Financial did a lot of fascinating and innovative things so if you're going to research Chinese fintech I would start with them.
Edit: I see what you're doing with the landing page approach, but you should gather conversion metrics. Advertise to your target market on Facebook and measure the CTR and signup rate.