How to Fill Out the Offsite Hosting Form
In order for your domain (URL) to work on your Pantheon site, will need to request to add a new "hostname" (domain/URL) via NetReg's Offsite Hostnames interface:
https://netreg.berkeley.edu/
After logging in and selecting the proper security contact from the dropdown, navigate to "Offsite Hostnames" in the left sidebar menu, and select "Add Offsite Hostname."