How to Check S/4 HANA SOAP standard API

Hi Team,

I got below API for customer invoice from API.SAP.COM. Can you please help me with steps to check this API in S/4 HANA system. I want to know underlying RFC or CDS which is getting used in this SOAP services. I tried SOAMANAGER but unable to figure out.

API Name:InvoiceRequest_Out

Thanks in Advance,

Girdhari