Many SAP projects require integration with external systems such as payment gateways, logistics platforms, mobile applications, cloud services, and third-party portals. I want to learn the complete process of sending data from SAP to an external REST API and reading the response in ABAP.

Please help with the following points:

• What is a REST API and how is it different from SOAP web services?
• How can we call a REST API from ABAP using CL_HTTP_CLIENT?
• How can we send GET, POST, PUT, and DELETE requests?
• How can we add HTTP headers such as Content-Type, Authorization, API Key, and Bearer Token?
• How can we send JSON data in a POST request from ABAP?
• How can we convert an ABAP structure or internal table into JSON format?
• How can we read and deserialize a JSON response into an ABAP structure?
• How can we handle HTTP response codes such as 200, 201, 400, 401, 404, and 500?
• How can we troubleshoot SSL certificate, authorization, timeout, and connection errors?
• What is the best way to store API URLs, credentials, and tokens securely in SAP?
• Can someone share a complete working ABAP example for calling a REST API and processing the JSON response?

A beginner-friendly explanation with complete ABAP code, error handling, and a real project example would be very helpful.