The best way is to build a product for a single customer, who will pay you upfront (early bird discount) for the solution with the agreement that it's your prod

The best way is to build a product for a single customer, who will pay you upfront (early bird discount) for the solution with the agreement that it's your product (not client work). Make that one customer super happy and then find more people that have the same problem you just built a solution for.