As you develop your strategy for monetizing APIs, a good place to start is by talking to your current API users. API Portals and other API engagement platforms are ideal not only for building a community but analyzing what APIs are successful. Ask the developers on the Portal what they believe is valuable and whether they would be willing to pay for it; sponsor a hackathon to gauge interest; and pay close attention to complaints about quality and ease of use.
Ensure your APIs are ready to scale and that they provide the level of security and protection end users will expect. And implement strong end-to-end governance for ongoing quality and top-of-the-line performance.