Sites created on one domain will not be available to add or secondary domain you need to change url of the site, to do that follow below steps : 

1. To do that first share site with public and then :


From the More drop-down menu, select Sharing and Permissions.

  1. In the text box, enter the email addresses of the people you wish to share your site with.
  2. Choose the level of access you wish to give them. (Anyone you set to Can view can look at the site. Anyone you set to Can edit can change the look and content of the site. Anyone you set to Is owner can change the look and feel of the site as well as make administrative changes, such as deleting the site or adding new owners.)
  3. The people whose email addresses you added will be sent an automated message when you add them unless you uncheck the box next to Notify people via email. If you choose to send the group a notification, you can add a personalized message. Simply write your message in the box below where you added the email address. You can also opt to have the invitation sent to you as well by checking the box next to Send a copy to myself.
  4. Click Share & save.

2. To Copy your site to a new URL :


Select That site and follow below steps :


Site, you can copy over the existing site to a new URL:

  1. Click the Gear menu  and select Manage site.
  2. Near the middle of the page, click Copy this Site.
  3. On the next page, choose a new name for your site and enter it under the "To" section in the box next to "Site name."
  4. By default, the new site will have your existing site's current sharing settings. You can prevent this by deselecting the box next to "Copy Site Collaborators". Revision history will not be carried over automatically from your existing site. Click the box next to "Include Revisions" to copy over revisions to the new site.
  5. Verify you are human by entering the distorted characters into the text box below it.
  6. Click Copy