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API monetisation includes both direct and indirect payment models to drive revenue. Free API is a popular way to provide access to an API as anyone can sign-up and start using the API. Free model works only in conjunction with other models, such as offering paid services to businesses with higher demands. Developer gets paid model has sub-models: Affiliate, Revenue Share, Points-Based, and Transactions Fee. API monetising is about how you expose the API to an audience while keeping it secure and controlling its consumption.