In the repository settings under the 'Webhook' tab, then select the webhook you added, there's a section that shows the recent deliveries. Also shows you the status of the recent delivery, with a possibility to retry it.

Once it's uploaded to git-pages, the old server is never tried for that domain. But you can confirm this by checking the `Server` header, it always mentions git-pages. Depending on `pages-server` in the `Server` header it's served by old pages. ~g