Java: Body of post request being sent as "NULL"

Question

I am trying to access the pricing data from an API via POST request with a string of SKU's.

The string to send the server is a JSON array of the SKU's with all spacing removed (provided under code).

I am receiving a 500 error from the server when accessing via Java/Eclipse, however, when sending similar requests via Postman I receive the desired response.

The API limits requests to 100 per response and I have over 6000 prices to populate so I don't want to do this via postman.

I will eventually write a loop to process the entire request, but before I can get there I need to figure out why the server is responding with a 500 code and stating that the body of the request is null.

Here is my code:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.nio.file.FileSystems;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.List;

public class PricingAPI {
    private static HttpURLConnection connection;

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        
//      This is the reader to interpret what comes from API
        BufferedReader readsFromURL;
//      String the API reader appends to
        String lineFromURL;
//      Content that gets read from API URL and will be written to our own file
        StringBuffer responseContent = new StringBuffer();
//      this is the String that hold the sku to request 100 after
        String skuStartAfter = "0";
//      This is the SKU list to request from the API Server
        List<String> jsonInputStringList;
//      Used to take the list of strings and convert to single string
        String jsonInputString;
//      This is the file the jsonInpustString pulls from
        Path skuList = FileSystems.getDefault().getPath("SKU.json");
        
        try {
//          This buffered reader pulls the text out of the JSON to be sent as body
            jsonInputStringList = Files.readAllLines(skuList);
            
//          Converts the list of strings to a single string
            jsonInputString = String.join("", jsonInputStringList);
            
//          Tests the content of the jsonInputString
            System.out.println(jsonInputString);
            
//              API Endpoint to send POST request to
                URL url = new URL("https://emerson-api.emersonecologics.com/pricing/v1/pricing-request/?limit=100&startAfterId=" + skuStartAfter + "&endsWithId=");
                
//              Opens connection and casts to HttpURLConnection
                connection = (HttpURLConnection) url.openConnection();
                
//              Tests the URL connection by printing it out for us to view
                System.out.println(url);
                
                
                
//              HTTP Request Setup
                
//              Set method to post
                connection.setRequestMethod("POST");
                
//              Allow output from API
                connection.setDoOutput(true);
                
//              Get the output stream and assign to 'os' variable
                OutputStream os = connection.getOutputStream();
                
//              Convert SKU JSON file to Bytes and put into an array
                byte [] input = jsonInputString.getBytes("utf-8");
                
//              Write byte array "input" to the output stream for body of the HTTP Request
                os.write(input, 0, input.length);
//              connection.setRequestProperty("Content-Type", "application/json; utf-8");
//              connection.setRequestProperty("Accept", "application/json");
                connection.setConnectTimeout(5000);
                connection.setReadTimeout(5000);
                
                
                
                
//              If there is an error this block runs
                if (connection.getResponseCode() > 299) {
                    readsFromURL = new BufferedReader(new InputStreamReader(connection.getErrorStream()));
                    while ((lineFromURL = readsFromURL.readLine()) != null) {
                        responseContent.append(lineFromURL);
                    }
                    readsFromURL.close();
                    
//                  Connection Status Indicator (200-500)
                    System.out.println(responseContent);
                    System.out.println(connection.getResponseCode());
                } 
//              If there is no error the content is added to responseContent
                else {
                    readsFromURL = new BufferedReader(new InputStreamReader(connection.getInputStream()));
                    while ((lineFromURL = readsFromURL.readLine()) != null) {
                        responseContent.append(lineFromURL.substring(163,lineFromURL.length()-52));
                    }
                    System.out.println(responseContent);
                    readsFromURL.close();
                }
            
        }catch (MalformedURLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
        

    }

}

here is the first 100 SKU's that I have as jsonInputString:

{"skus":["A16411","A16413","A16723","A16735","A16722","A16904","A16738","A16747","A16750","A34989","A16726","A16415","A16725","A16936","A16418","A16412","A16739","A16934","A16933","A64049","A67071","A67064","A16705","A16403","A16937","A16704","A16941","A16703","A16414","A16733","A16724","A66501","5HYDR","A71901","A7060","ACG16","ACET2","ACETY","AR70461","ADRE3","A70760","A70102","ALAR60","AIDII","A69109","A77490","ANTIO","ARTEM","ART33","ARTHR","A77510","A65702","A65603","A72809","BIFID","BIOTI","A76510","A71604","A76440","BRAI2","REMIN","BUFCC","BUF21","A50203","BUFCP","BUTYR","CALC2","CMCI2","PYRUV","CALM","CALM1","A72007","A74704","CAT4","CELLU","CHMVM","CHITO","CHRON","COQ30","COQ12","COMPL","COPP2","COQGA","COQ52","CQTOC","CQH60","A72908","A68802","AR76670","DHA8","DHE30","DHE31","DHE14","DHE11","DIM2","DIM5","DIM4","DRWI2","EARTH","A77100"]}