Click Chat with Support and provide Blackbaud with the full URL you intend to use and name of the product that the URL will be used for. 
 
If a custom URL has not been enabled for your hosted application, use the default URL for your application (replace SiteID with your own Blackbaud Site ID):
  • Faculty Access for the Web: [SiteID]FAWeb.blackbaudondemand.com
  • NetClassroom: [SiteID]NetClass.blackbaudondemand.com
  • WebPurchasing: [SiteID]WebPurchase.blackbaudondemand.com
NOTE: After the URL has been enabled, users who access the application through the custom URL may receive a security warning in their browser due to the URL on the site's security certificate not matching the custom URL.  Blackbaud will not install another domain's certificate. Issues related to using a custom URL are beyond our scope of support.