Document Approval API via CIG?

Hi All,

We are planning to use Ariba Document Approval API for a planned Fiori My Inbox <> Ariba integration to handle approvals. My current understanding is that CIG does not handle/execute API calls (since the CIG documents - Installation, Overview and Config does not state this API). Is that correct?

Or we still need a middleware to execute the API?

Also, if do we have any documentation that states CIG cannot process APIs?

Apologies on the bulk of questions.