In this article, i will share you how to make interface webservice with sender is SOAP adapter and Receiver with REST adapter scenario, hope can help you to implement SAP PO.
In this demonstration, i will make simple login function call from SAP ERP to third party using REST and HTTP.
Enterprise Service Builder
Design data type
Design message type
Design service interface
Design message mapping
Design operation mapping
Integration Builder
Define SOAP sender channel
Define REST receiver channel
Define Integrated Configuration Object
Enterprise Service Builder
Design data type
Data type for SAP sending request
Data type for SAP response request
Data type for Legacy sending request
Data type for legacy response request
SAP Sending request SAP response requestLegacy sending requestLegacy response request
Design message type
for each data type, you can define message type as well
Define service interface
Outbound service interface and note that is synchronous message interfaceInbound service interface
Define message mapping
Request message mapping, here you can do mapping per your require as wellResponse message mapping
SOAP Sender channel , in this example scenario sender is SAP ERP or SAP CAR via Abap proxy
REST receiver channel
REST receiver channel general. REST webservice hosted can be HTTP or HTTPS. With HTTPS you need install client or server certification on SAP PO. I will show you how to install SAP PO certificate on another topic. REST provider’s Endpoint (URL)REST Operation. REST protocol standard work through HTTP operation method, example : POST, GET, DELETE etc. You can search REST standard methods on Internet. Methods identify by REST webservice provider.REST Data format. Normally, REST adapter send and receive data via JSON format. In REST channel, you need convert data from XML to JSON for request messages and JSON to XML for response messages.
SAP Zero to Hero 
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