In your GitHub repository, navigate to the repository settings tab by clicking as shown here and then click on Webhooks. You may need to enter your password again:
A green tick should be shown against the Webhook you created. If not, click Edit to show the details and scroll down to the Recent Deliveries. Here is an example of one which failed earlier:
Click on the ellipsis to show the details of the error. Here are a few known resolutions:
1. GitHub Webhook reports a response of 403 (a successful deployment produces a 200 response)
A 403 is returned when the request is not allowed. The response body should contain an HttpException with the text "Not Allowed"
The Git Deployment Hub interface will also have a status of "Pending".
In Git Deploy Hub, check the parameters listed against the Pending action. Note down the address. It might be something similar to 22.214.171.124.
Edit the web.config file. Add the generalised form of this address to the <gitDeployHub allowedAddresses section. For example, for this address of 126.96.36.199 enter 192.30.*.*. This will ensure that whichever GitHub server fires the webhook, the Deployment Hub will allow it.
2. GitHub Webhook reports a Service TimeoutResolution
Check that the Webhook URL is correct.
Check that the target system web site is started.
Check that the Hub can be accessed on the Target system.
Check the Deployment State in the Hub.