In order to reference the Velaro thank you page with a custom Unavailable to Chat survey, do the following:
Login to the Velaro control panel: http://login.velaro.com
Navigate to: Surveys > Edit
Select your custom Missed Chat (Unavailable to Chat) survey
Find the "Current Redirect:" field
Press "Select New"
Enter in the following URL:
http://service.velaro.com/visitor/EmailStatus.aspx?EmailStatus=Success&siteid=YOUR_SITE_ID_HERE