Get API response error message using Web Client Mono in Spring Boot

I am using webflux Mono (in Spring boot 5) to consume an external API. I am able to get data well when the API response status code is 200, but when the API returns an error I am not able to retrieve the error message from the API. Spring webclient error handler always display the message as

ClientResponse has erroneous status code: 500 Internal Server Error, but when I use PostMan the API returns this JSON response with status code 500.

{
 "error": {
    "statusCode": 500,
    "name": "Error",
    "message":"Failed to add object with ID:900 as the object exists",
    "stack":"some long message"
   }
}

My request using WebClient is as follows

webClient.getWebClient()
            .post()
            .uri("/api/Card")
            .body(BodyInserters.fromObject(cardObject))
            .retrieve()
            .bodyToMono(String.class)
            .doOnSuccess( args -> {
                System.out.println(args.toString());
            })
            .doOnError( e ->{
                e.printStackTrace();
                System.out.println("Some Error Happend :"+e);
            });

My question is, how can I get access to the JSON response when the API returns an Error with status code of 500?

Look at .onErrorMap(), that gives you the exception to look at. Since you might also need the body() of the exchange() to look at, don't use retrieve, but

.exchange().flatMap((ClientResponse) response -> ....);