Getting null values on json object read from CloseableHttpResponse using Jackson, but also getting 200

Making a request which returns a json response body fine in Postman, but just returns a 200 when I run my code. I'm pretty sure the classes I'm using to deserialize with Jackson are structured correctly, and the json body of the request appears to be valid. What am I missing?

Here's the class where the request is made:

import ...

@Service
public class CPService {

    @Value("${cp.url}")
    private String cpUrl;

    @Autowired
    private ObjectMapper objectMapper;

    public ResponseData send(String caseId, String pId, String documentId) throws IOException {
        String version = "1.0";

        Request request = Request.builder()
                .requestData(RequestData.builder()
                        .version(version)
                        .transactionId(caseId)
                        .credPublish(CredPublish.builder()
                                .refId(pId)
                                .reportDocumentId(documentId)
                                .build())
                        .build())
                .build();

        HttpPost httpPost = new HttpPost(cpUrl);
        EntityBuilder builder = createBuilder();
        builder.setContentType(ContentType.APPLICATION_JSON);
        builder.setText(objectMapper.writeValueAsString(request));

        httpPost.setEntity(builder.build());

        try (CloseableHttpClient httpClient = createHttpClient()) {
            CloseableHttpResponse response = httpClient.execute(httpPost);
            ResponseData responseData = objectMapper.readValue(response.getEntity().getContent(), ResponseData.class);
            return responseData;
        }
    }

    EntityBuilder createBuilder() {
        return EntityBuilder.create();
    }

    CloseableHttpClient createHttpClient() {
        return HttpClients.createDefault();
    }
}

Here are the classes used:

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import lombok.Data;
import lombok.Getter;
import lombok.Setter;

import java.util.List;

@Data
@Getter
@Setter
@JsonIgnoreProperties(ignoreUnknown = true)
public class ResponseData {
    private Integer resultCount;
    private String version;
    private CredPublishResponse credPublish;
    private String transactionId;
    private List<ErrorMessage> errors;
}

import lombok.Data;
import lombok.Getter;
import lombok.Setter;

@Data
@Getter
@Setter
public class CredPublishResponse {
    private String responseMessage;
}

Here is an example of the response from Postman:

{
    "responseData": {
        "resultCount": 1,
        "version": "",
        "credPublish": {
            "responseMessage": "success"
        },
        "transactionId": "CASE-1234567"
    }
}