Facebook webhook Application creation fails due to "inability to verify the provided URL"

Question

Unable to create a Facebook Webhook application due to the error "could not verify the provided URL"

• Callback URL works fine with browser with port 443 https

• Servlet code for receiving a mail call from a web host, as shown below

      protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
           System.out.println("**************Entering Callback Servlet**************************");
              Map<String, String[]> parametersMap = request.getParameterMap();
              if (parametersMap.size() > 0) {
                  if (request.getParameter("hub.mode").equals("streamInit")) {
                      System.out.println("Verify Token: " + request.getParameter("hub.verify_token"));
                      System.out.println("Challenge number:" + request.getParameter("hub.challenge"));
                      String responseToClient = request.getParameter("hub.challenge");
                      response.setStatus(HttpServletResponse.SC_OK);
                      response.getWriter().write(responseToClient);
                      response.getWriter().flush();
                      response.getWriter().close();           
                      response.getWriter().append("Fetch-Mode").append(request.getParameter("hub.mode"));
                      response.getWriter().append("App Verify Token:").append(request.getParameter("hub.verify_token"));
                      response.getWriter().append("App Challenge No").append(request.getParameter("hub.challenge"));
                      System.out.println("**************Callback Successful**************************");
                     }
  
                  //response.getWriter().append("Served at: ").append(request.getContextPath());
                  }else{
                      System.out.println("**************Not an Facebook POST**************************");
                  }
                 System.out.println("**************Exiting Callback Servlet**************************");
  
  
          }
  
  
  
  protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
              doGet(request, response);
          }
  

Need help with what I'm missing here.

Answer 1

Facebook , (: callback.php), mod rewrite. , https:// (, comodo).

Answer 2

https://ngrok.com/, https Webhooks localhost dev.

if (request.getParameter("hub.mode").equals("streamInit"))

to

if (request.getParameter("hub.mode").equals("subscribe"))

.