As Ashley has previously said, there are so many different monetization APIs that it would be easier to contact the relevant one and get them to create a plugin, as they already know their API. Otherwise, you will need a good understanding of javascript and the relevant skill to do this yourself. There is no 'tutorial' for creating API plugins.
You could post a request in the Extending C2 section to see if one of the current plugin devs would be interested in developing this. It doesn't hurt to ask.