Hi,
I am an SAP certified developer with 6+ years of experience of ABAP, Gateway and UI5. I have extensive experience of creating a RESTful OData services in SAP and consuming any 3rd party REST API within SAP using ABAP.
I can create a report which can be run with multiple selection criteria and and on user action, POST this data to the REST API. Does your API really need a file or JSON data is fine? Please ping me to discuss further.
BR, Ekansh