If you have already linked your Cloud Drive to Sync, you may just need to press the button a second time. If it is your first time synchronizing or retrieving files from the Sync website, the pop-up window might have blocked by the browser.
To disable your pop-up blocker for Sync:
Chrome: Click the menu button, then select Settings > Advanced > Privacy and security > Site settings > Pop-ups and redirects, and add “sync.vive.com” under Allowed.
Firefox: Click the menu button, then select Options > Privacy & Security, and uncheck the box to the left of “Block pop-up windows”
Support for Safari is coming soon.