The third party and other SAP applications can access RFCs in a multiple
ways.
1. Exposing RFC as a web-service using SAP Process Integration (PI/PO)
2. Direct ALE connection between other SAP systems in the same landscape.
3. Exposing RFC as a web service using transaction SE37 (Utilities)
Configuration Steps How to Expose RFC as a Web Service using PI/PO.
1. Make sure your function module or the API is “Remote enabled”.
Import RFC to SAP PI.
2. Create input, output data types and message types which correspond to SOAP input and output data
formats.
3. Create message mapping for SOAP request to RFC input.
Block Diagram of SOAP to RFC Scenario
This example third party sender uses webservice call to connect to SAP PI/PO via SOAP adaptor and PI
converts that call to RFC call and connects to ECC and executes function module in ECC and returns data
back to PI/PO and PI/PO intern return that message back to calling webservice.
Link: https://learnsapintegration.com/step-by-step-procedure-to-implement-soap-to-rfc-synchronousscenario-in-pi-po/