How to call Servlet/Sling model for Custom Action type in Forms

Hi, 

I have created custom form action to invoke third party API after submitting the AEM form container. Now I want to call the Servlet which will have code for the api call. When I select custom action in the form container it asking for the id. Plese help.

and here is my sevlet code

package com.adobe.aem.FormsDemo.core.servlets;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParser;
import org.apache.http.HttpEntity;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;
import org.apache.sling.api.SlingHttpServletRequest;
import org.apache.sling.api.SlingHttpServletResponse;
import org.apache.sling.api.servlets.HttpConstants;
import org.osgi.framework.Constants;
import org.osgi.service.component.annotations.Component;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.servlet.Servlet;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.URL;

@Component(service = Servlet.class, property = { Constants.SERVICE_DESCRIPTION + "=JSON path based servlet",
        "sling.servlet.methods=" + HttpConstants.METHOD_GET, "sling.servlet.paths=" + "/bin/postservletexample" })public class CustomServlet {
    protected void doPost(SlingHttpServletRequest request, SlingHttpServletResponse response) {
            try {
                URL url = new URL("https://mocki.io/v1/8a06b1d3-cda3-4e9e-a767-fdc662311718");
                HttpURLConnection connection = (HttpURLConnection) url.openConnection();
                connection.setRequestProperty("accept", "application/json");
                int status = connection.getResponseCode();
                System.out.println(status);
                if (status!=0){
                    response.getWriter().write("Success");
                }else{
                    response.getWriter().write("Failed");
                }
                // response.setStatus(SlingHttpServletResponse.SC_OK);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }