In modern application security, JWT (JSON Web Token) has become a widely adopted standard for authentication and authorization due to its simplicity and effectiveness. However, when implementing JWT in Spring Security, you might encounter issues where the application fails to generate or receive the token as expected. These issues can stem from multiple factors, including configuration mistakes, missing headers, or incorrect token validation. This article will address these problems in detail, provide code examples, and explore practical solutions to ensure a smooth JWT authentication process.