Now in this last part we will add the custom domain!
When the DNS zone has been updated and redirected, verify first, it’s time to update your app service.
Head over to the App Service and note hostname and IP.

Go to the DNS Zone and add an A-record with @ that redirects to the IP-adress of your web app and a TXT for the hostname for your azure sites hostname.

Now go back into the App Service to custom domain and validate.

There you go! A custom hostname for your app service!