Brother use your ngrok url: https://13bcfd61e6cd.ngrok.io/webhooks/facebook/webhook/
If your url is working fine then why are you changing it. I used xxxxxxxxxx just for reference.
Have you tested your messanger after you get the success status 200 ok
Note when your app is in development mode
Only admin, developer and tester can get messages from chatbot
You can this in Roles section of your fb app