I started with a couple of common ideas that we always had to implement for a lot of clients and I built a couple of simple Django-based services on Digital Ocean, in the free time I had from taking care of my newborn.
Therefore right now I'm running:
- https://getgeoapi.com: a GeoLocation API with additional data
- https://currency.getgeoapi.com: a Currency Conversion API
I'm terrible at marketing, so what I did was to leverage existing marketplaces. Slowly, over months, I started to build a reputation and build a userbase.
Profits range between 1000$-1800$ and I'm planning to expand to other marketplaces (I have a lot of customer who are on Shopify, even if I don't offer a Shopify app) and build other APIs. Hopefully I'll have more time once my sons go to nursery / school.
I use Stripe for direct sales on the website and RapidAPI (ex Mashape) as a marketplace.
I can't say RapidAPI is been smooth sailing: their payment processing is riddled with fees (thanks PayPal) and there are frequent outages and issues with their proxy. Still, I think using a marketplace can be a decent approach for developers who don't want to spend their days on reddit or finding their clients.