Any advice for a new crowdfunding platform about to go live and how to grow my following and gather pilot users?

Hi everyone! Any advice would be really helpful. I spent months building this awesome crowd funding platform that’s geared towards social impact. Think of GoFundMe meets chuffed meets buy me a coffee. The platform is fully tested and ready to go and is live but behind a password wall until we gather enough users to unleash. Our budget is incredibly limited so we want to go to the viral organic route. Any suggestions, recommendations, on how to build my following on Instagram and get users, specifically activists, advocates, and nonprofits to register and poke around.

Thanks in advance!