Rasa + Slack + EC2 instance

Hello All, I am trying to connect my rasa chatbot with slack and EC2 , I want to use the EC2 instance ip address to connect with rasa chatbot through slack. I have connected the chatbot and created an account in slack when I am tryin to connect to the Event Subscriptions it is not getting connected to it and showing .

Your URL didn't respond with the value of the challenge parameter.

http://<ip>:<port>/core/webhooks/slack/webhook ip :- it is of EC2 instance private address port :- 5005 where the rasa server is running.

Can anyone please help me out with this.

Thanks!!!