Spring Boot ExceptionHandler for MethodArgumentNotValidException in RestController never gets invoked

I'm using Spring Boot v2.2.10 and Spring v5.2.9. I've created a Rest controller with an @Valid @RequestBody annotation. The validation works fine (I get a 400 BAD REQUEST response when submitting values outside of the constraints), but I don't like the default error message as it reveals too much of internals. Thus, I defined an @ExceptionHandler(MethodArgumentNotValidException.class) method, but this method never gets invoked.

This is the controller with the exception handler:

import java.util.List;
import java.util.stream.Collectors;

import javax.validation.Valid;

import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.validation.ObjectError;
import org.springframework.web.bind.MethodArgumentNotValidException;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseStatus;
import org.springframework.web.bind.annotation.RestController;
import lombok.RequiredArgsConstructor;


@RestController
@RequiredArgsConstructor
@RequestMapping("/api/data")
public class DataController {

    @PostMapping(path = "/{id}", consumes = MediaType.APPLICATION_JSON_VALUE)
    private void postData(
            @PathVariable String id,
            @Valid @RequestBody MyDTO dto) {
        
        // DO SOMETHING

    }
    
    @ResponseStatus(HttpStatus.BAD_REQUEST)
    @ExceptionHandler(MethodArgumentNotValidException.class)
    public List<String> handleValidationExceptions(MethodArgumentNotValidException ex) {
        System.out.println("Handling method argument not valid exception");
        return ex.getBindingResult()
            .getAllErrors().stream()
            .map(ObjectError::getDefaultMessage)
            .collect(Collectors.toList());
    } 
}

The DTO:

import javax.validation.constraints.Max;
import lombok.Getter;

@Getter
public class MyDTO {
    
    @Max(value = 1, message = "Value should not be greater than 1")
    private float value;
    
}

I also tried to put the ExceptionHandler into an extra class:

// Imports

@Order(Ordered.HIGHEST_PRECEDENCE)
@RestControllerAdvice
public class GlobalExceptionHandler {

    @ExceptionHandler(MethodArgumentNotValidException.class)
    // Same as before

}

As I've said, my ExceptionHandler never gets invoked. What might I be doing wrong?