Integration of Opportunity to external app via web service

Summary:

There is a need to POST an opportunity ID to the external app via API after clicking save. Does this need to go through OIC or can be direct from Webservices and add an "after create" trigger to call the API ?

Scenario is a opportunity record is created and upon saving the record, the API will be triggered and sends the attribute to the target application via their API. 

Flow is only outbound from CX to Sharepoint