Generating Swagger UI from java, providing example for a RequestBody doesn't work

how do I provide an example for the body of a request in my Swagger UI? I am using Springboot as a framework. This is the smallest java code to reproduce the problem:

import org.springframework.http.ResponseEntity;
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.RestController;

import io.swagger.v3.oas.annotations.Operation;
import io.swagger.v3.oas.annotations.media.Content;
import io.swagger.v3.oas.annotations.media.ExampleObject;

@RestController
@RequestMapping("/api/my/problem")
public class MyProblemResource {

    @PostMapping(value = "/")
    @Operation(summary = "Create person")
    public ResponseEntity<PersonDTO> getPerson(
            @io.swagger.v3.oas.annotations.parameters.RequestBody(
                    description = "the person you want to create, in json format",
                    content = @Content(examples = @ExampleObject( value = "foobar"))
                    )
            @RequestBody PersonDTO person){
        return ResponseEntity.ok().build();
    }
}

class PersonDTO{
    String firstName;
    String lastName;
    public PersonDTO() {}
    public String getFirstName() {
        return firstName;
    }
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }
    public String getLastName() {
        return lastName;
    }
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }
}

So I would expect the string "foobar" to appear in the generated Swagger UI, but it doesn't: the text in the black box should be "foobar"

Edit: I've also tried putting the annotation at the method level as suggested by https://stackoverflow.com/users/1076463/robin, like this: https://pastebin.com/FPGHuYKd , still no luck.

By the way, those annotations come from a dependency in my Maven pom.xml :

        <dependency>
            <groupId>io.springfox</groupId>
            <artifactId>springfox-boot-starter</artifactId>
            <version>3.0.0</version>
        </dependency>