Understanding on MDM

We are doing integration of Master data governance over cloud.

I opted to publish standard odata services on sap pi like API_BUSINESS_PARTNER that will allow third party caller to do CRUD operations.But I need to provide sample json data to them in order to do so which they will send as request to our pi server.How to provide them this data as merely providing one entity set data using a GET request and using same as a POST request does not fulfill the purpose here.I need proper trace of complete transaction for input request.
I am of inclination that standard fiori apps must be using these standard odata services.Suppose I use standard fiori app to create vendor.How to know data request ?Service like API_BUSINESS_PARTNER use SADL concept of CDS and I am not so sure how will I get trace.
I have to do such activities for more than 10 standard odata services to get right payload data that will allow master creation within system.Can you throw some hint on that?