We have a well documented API which you can reference, but which requires a developer to use. All our API documentation is here: https://api.metropublisher.com
We provide a Quickstart guide to the API here: https://api.metropublisher.com/quickstart.html
To generate the key, you just need to log on to your site at go.metropublisher.com and click on the API link at the top right above your site edit buttons. You must have the highest level user permissions to do so.
This is our API Google Group where technical questions can be submitted directly to the development team. Those are generally answered very quickly. Here is a link to sign up to the API Google group: https://api.metropublisher.com/doc/help.html