Spring Rest Controller

@RestController("/api")
public class LoginRegRest {
    @Autowired
    private UserService userService;

    @PostMapping("/login")
    public ResponseEntity<String> login(@RequestBody LoginRequest request) {
        return ResponseEntity.ok("Success!");
    }

    @PostMapping("/registration")
    public ResponseEntity<String> registration(@RequestBody RegistrationRequest request) {

        System.out.println("Controller is working!");

        userService.registerUser(request);
        return ResponseEntity.ok("Success!");
    }
}

Java Script Code

$(document).ready(function() {
  $("#registrationForm").submit(function(event) {
      event.preventDefault(); 

      const user = {
          username: this.username.value,
          email: this.email.value,
          password: this.password.value,
      };

      $.ajax({
          type: "POST",
          url: "/api/registration",
          data: JSON.stringify(user),
          contentType: "application/json",
          success: function(response) {
              // Nothing
          },
          error: function(xhr, status, error) {
              var errorMessage = xhr.responseText;
              alert("Error: " + errorMessage);
          }
      });
  });
});

Spring version: 3.3.2

I checked absolutely everything I could. Give me reasons why RestController might not fire when sending a registration request!