• What is an API?
• Why is API Testing Important?
• Advantages of API Testing
• Disadvantages or Challenges of API Testing
• Differences between API Testing, Unit Testing, and Integration Testing
• Overview of XML 
• Overview of JSON
• Comparison between XML and JSON
• What are API Methods?
• What are HTTP Status Codes?
• What is Web Service Testing?
• Difference between API and WebService Testing
• Types of APIs:
• Request Headers and Parameters
• Authentication and Authorization
• API Keys for API Testing
• OAuth Keys for API Testing
• JWT (JSON Web Tokens) for API Testing
• Creating Test Cases for API Functional Testing 
• Advanced API Testing Techniques
• Mocking and Stubbing APIs using postman api
• Contract Testing for APIs
• Overview of Popular API Testing Frameworks
• API Testing Best Practices