My side project is gaining users slowly everyday. It's called noteshred and it allows to you send people self shredding, encrypted notes with unique URLs, http

My side project is gaining users slowly everyday. It's called noteshred and it allows to you send people self shredding, encrypted notes with unique URLs, https://www.noteshred.com https://www.noteshred.com. I'm curious to know how you guys transitioned from a free tool to something that generated income. I can't imagine advertisements wouldn't bring in much revenue, so how did you go about introducing a paid model?