SOAP

SOAP - Simple Object Access Protocol.

Standard messaging protocol.

Mature, comprehensive, and XML based.

It is used heavily in financial services and payment gateways, where security and reliability are key.

Not so good for a lightweight mobile app or a quick prototype. SOAP might be overkill due to its complexity and verbosity.

The link given below will help you to understand how SOAP API works.

https://documenter.getpostman.com/view/8854915/Szf26WHn#e412b255-3fea-442a-a986-128114ce5a7bdocumenter.getpostman.com

Example SOAP Request

POST /WebService.asmx HTTP/1.1
Host: www.example.com
Content-Type: text/xml; charset=utf-8
Content-Length: nnnn
SOAPAction: "http://www.example.com/SomeWebService/SomeWebMethod"

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
               xmlns:xsd="http://www.w3.org/2001/XMLSchema"
               xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
  <soap:Body>
    <SomeWebMethod xmlns="http://www.example.com/SomeWebService">
      <Parameter1>Value1</Parameter1>
      <Parameter2>Value2</Parameter2>
    </SomeWebMethod>
  </soap:Body>
</soap:Envelope>

SOAP Response

HTTP/1.1 200 OK
Content-Type: text/xml; charset=utf-8
Content-Length: nnnn

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
               xmlns:xsd="http://www.w3.org/2001/XMLSchema"
               xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
  <soap:Body>
    <SomeWebMethodResponse xmlns="http://www.example.com/SomeWebService">
      <SomeWebMethodResult>ResultValue</SomeWebMethodResult>
    </SomeWebMethodResponse>
  </soap:Body>
</soap:Envelope>