Note - I use heroku for deploying prod app and for local I use smee for proxying webhook payload to localhost.
- Deploy the probot app code to heroku.
- Create two github apps say my-app and my-app-dev.
- For my-app put the heroku url like http://my-app.herokuapp.com/ in Webhook URL.
- For my-app-dev put the smee url like https://smee.io/aldnhksfh in Webhook URL.
- For both apps use appropriate Webhook Secrets and download the private keys.
- Rename the private keys to private-key.pem and private-key-dev.pem respectively.