How to validate an idea before start developing?

Hello guys, greetings from Cuba! Days ago, I've trying to validate an idea for a product to help people by creating a Remittance and Donation tool that anyone can use to convert himself into an R&D agent. Basically is a Peer-To-Peer tool, but I've found a couple of communities where I discuss my project idea. So, the question is, which communities and platforms do you recommend to validate and improve an idea? I know a few: - Indie Hackers - Product Hunt (using discussions) - Reddit communities - Slyk.io (to create a coin-powered community and reward your community for contributing good ideas)