I've built a web app, now what?

So I recently launched a web app. It's free to use as of right now but I'm thinking of ways to monetize it.
I tried adding Google ads to it, but I was rejected, I think it's because I don't have enough traffic yet? I also tried using Media.net and was rejected from there too.

It's not an adult website or anything like that, it's essentially a tool for a website.
I've seen a couple of similar websites that was approved of ads, so I'm going to assume it's because I don't have enough traffic yet.

I'm getting roughly 100 unique visitors a day and it's only day 3 so I think it's going well so far?
I've only posted it on Reddit so far.

What are some ways I could monetize it? Having people pay a subscription fee seems.. I don't know, my competitors already do that with super low prices.

I appreciate your help

Google won't approve you for a contentless site. It's likely those adsense accounts were approved for different sites, then after that google doesn't really care what other sites are added unless they start manually reviewing you for suspicious stuff or they're running a different network that runs adsense mixed in with their own ads. Go to sites like yours, click the adchoice icon on the banners and see what ad network it is. Most probably aren't google directly.

care to share your web app to check it out?

What does your app actually do?
Do you have much content on your site, terms of use, privacy and all that?

Monetize with IAP, sell premium features (e.g. get >100 items/queries for $10)