I'm working on the Trailhead "Build a Community with Knowledge and Chat" because I really want to learn how to use the Chat Snap ins for communitites. I'm getting stuck on the "Create a Chat Snap-in" section. It says to go to the Visualforce pages and copy just the beginning of the address which is https://c.na35.visual.force.com/apex/CommunitiesTemplate. So I am copying  https://c.na35.visual.force.com. Then it says to create a new CORS with this copied address. However, when I copy this into the new CORS original URL pattern then it will not save. Can anyone tell me what I am doing wrong? I can't move forward without this step and I really want to learn how to do this. Thank you!