S        This expression returns the expiry time of the currently loaded SSL/TLS certificate.

It takes two parameters:

  1. The first parameter is either 0 for the expiry time to be in the server machine's local timezone, or 1 for the expiry time in UTC timezone.
    You probably want 0.
  2. Format of date time.
    You can pass "" for the default datetime format, which is:
    "%I:%M:%S%p on %A %d %B %Y"
    …which translates to:
    "11:23:45PM on Sunday 03 January 2022"
    Otherwise, you can use a custom format in strftime. Both C++11 and C++17 strftime modifiers are supported.


You can use this expression when a certificate is loaded, even when the Secure WebSocket Server is not hosting.

If no certificate is loaded, then the expression will return:

Secure WebSocket server not hosting

If the custom format you give is broken, the expression will return:

Format "(your strftime format)" is invalid


No On Error event will be generated for either of these errors.