API Endpoint Returns 404 on Replit

1. Controller not annotated with @RestController or method with @GetMapping/@PostMapping
2. Wrong HTTP method (GET vs POST)
3. Route path mismatch between client and server
4. Controller class not in Spring-scanned package
5. Typo in request URL or path variable

Ensure @RestController on class and @GetMapping('/path') on method. Check request method matches (GET, POST, etc.). Verify full URL including host matches Replit deployment domain. Use Postman to test endpoint. Check Spring logs for registered endpoints with ./gradlew bootRun --debug | grep RequestMapping.