Closing a gallery is to manually make the photos inside that project inaccessible to your clients. While expiry date automatically closes a gallery on the date set by you.

Choose any gallery you wish to close manually. Navigate to the left side column and find Gallery Settings. Toggle to General Gallery Settings on the top. The last option reads Close Gallery which will immediately make the gallery unavailable for client. So when the client opens the master link provided, they are notified that the gallery has been closed and that they should directly contact you to resolve the discrepancy.

After the gallery has been closed, use the same procedure and button to reopen gallery and reset your expiry date accordingly.