HTTP post with JSON body using JAVA

I'm using JAVA to try send a HTTP post via Java to Insight (Our cloud CMDB).
For some reason, I'm getting a HTTP error 400, and I can't seem to find the issue, and I can't find out how to retrieve the error message from the HTTP call.

package com.cmdbsync.app;

import java.io.IOException;

import com.google.gson.Gson;

import org.apache.http.Header;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClientBuilder;

import static org.hamcrest.Matchers.equalTo;
import static org.hamcrest.MatcherAssert.assertThat;
    
public class App 
{
    public static void main( final String[] args ) throws IOException, InterruptedException
    {
        String pc_data_json = "{" + 
                "\"objectTypeId\": \"90\"," +
                "\"attributes\": [{ " +
                    "\"objectTypeAttributeId\": \"365\"," +
                    "\"objectAttributeValues\": [{" +
                        "\"value\": \"<PC name>\"" + // PC name
                    "}]" +
                "}," +
                "{" +
                    "\"objectTypeAttributeId\": \"548\"," +
                    "\"objectAttributeValues\": [{" +
                        "\"value\": \"<PC serial>\"" + // PC serial
                    "}]" +
                "}," +
                "{" +
                    "\"objectTypeAttributeId\": \"380\"," +
                    "\"objectAttributeValues\": [{" +
                        "\"value\": \"CM-283\"" +
                    "}]" +
                "}," +
                "{" +
                    "\"objectTypeAttributeId\": \"381\"," +
                    "\"objectAttributeValues\": [{" +
                        "\"value\": \"CM-284\"" +
                    "}]" +
                "}," +
                "{" +
                    "\"objectTypeAttributeId\": \"383\"," +
                    "\"objectAttributeValues\": [{" +
                        "\"value\": \"4\"" +
                    "}]" +
                "}]" +
            "}";
            
        Gson gson = new Gson();
        StringEntity entity = new StringEntity(gson.toJson(pc_data_json));

        // HTTP calls
        CloseableHttpClient httpClient = HttpClientBuilder.create().build();

        try {
            HttpPost request = new HttpPost("https://insight-api.riada.io/rest/insight/1.0/object/create");
            request.setHeader("Content-Type", "application/json");
            request.setHeader("Authorization", "Bearer <api key>");
            request.setEntity(entity);

            CloseableHttpResponse response = httpClient.execute(request);

            System.out.println("Request");
            Header[] headers = request.getAllHeaders();
            for (Header header : headers) {
                System.out.println("Key: " + header.getName() + ", value: " + header.getValue());
            }

            System.out.println("Response");
            Header[] header = response.getAllHeaders();
            for (Header head : header) {
                System.out.println("Key : " + head.getName() + " , value : " + head.getValue());
            }
            
            assertThat(response.getStatusLine().getStatusCode(), equalTo(200));    

        } catch (Exception e) {
        } finally {
            System.out.println("Done");
        }
    }
}

The pc_data_json string should be correct - the reason for how this is made, is because I've to import ~700 PCs and therefore will run this through a loop reading a .csv file and therefore want to be able to change PC name and PC Serial.

This is my output when calling the program

Picked up JAVA_TOOL_OPTIONS: -Djava.vendor="Sun Microsystems Inc."
Request
Key: Content-Type, value: application/json
Key: Authorization, value: Bearer <api key>
Response
Key : Server , value : nginx/1.14.0
Key : Date , value : Mon, 04 May 2020 08:43:21 GMT
Key : Content-Type , value : application/json
Key : Content-Length , value : 883
Key : Connection , value : keep-alive
Key : X-Content-Type-Options , value : nosniff
Key : X-XSS-Protection , value : 1; mode=block
Key : Cache-Control , value : no-cache, no-store, max-age=0, must-revalidate
Key : Pragma , value : no-cache
Key : Expires , value : 0
Done
Exception in thread "main" java.lang.AssertionError:
Expected: <200>
     but: was <400>
        at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:20)
        at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:8)
        at com.cmdbsync.app.App.main(App.java:83)

Hopyfully some wizard in here can help me!