SerwerSms - api post call

@Configuration
public class WebClientConfiguration {

    @Bean
    public WebClient.Builder getWebClientBuilder() {
        return WebClient.builder();
    }
}

@Service
public class SmsService {

    @Autowired
    private WebClient.Builder webClientBuilder;

    private static String URI = "https://api2.serwersms.pl/messages/send_sms";


    public SmsResponseDto send(String phone) {

        SmsGateway smsGateway = new SmsGateway();
        smsGateway.setLogin("mojUser");
        smsGateway.setHaslo("mojeHaslo");
        smsGateway.setNadawca("nadawcaTekst");
        smsGateway.setNumer(phone);
        smsGateway.setWiadomosc("this is the test message");

        return webClientBuilder.build()
                .post()
                .uri(URI)
                .contentType(MediaType.APPLICATION_JSON)
                .body(BodyInserters.fromValue(smsGateway))
                .retrieve()
                .bodyToMono(SmsResponseDto.class)
                .retryWhen(Retry.fixedDelay(2, Duration.ofMillis(100)))
                .block();
    }

@Data
public class SmsGateway {
    @JsonProperty
    String login;

    @JsonProperty
    String haslo;

    @JsonProperty
    String nadawca;

    @JsonProperty
    String wiadomosc;

    @JsonProperty
    String numer;
}

    public SmsResponseDto send() {

        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_JSON);

        Map<String, String> map = new HashMap<String, String>();
        map.put("username", "user");
        map.put("password", "pass");
        map.put("phone", "+48555666555");
        map.put("text", "test from Spring Boot");
        map.put("sender", "John-Doe");

        return webClientBuilder.build()
                .post()
                .uri(URI)
                .accept(MediaType.APPLICATION_JSON)
                .contentType(MediaType.APPLICATION_JSON)
                .body(BodyInserters.fromValue(map))
                .retrieve()
                .bodyToMono(SmsResponseDto.class)
                .retryWhen(Retry.fixedDelay(2, Duration.ofMillis(100)))
                .block();
    }