Use SendNotify to notify other client applications about event you want to notify them. See Notify demo project sources for details.
Name of the notification channel to be signaled (any identifier).
The "payload" string to be communicated along with the notification. This must be specified as a simple string literal. In the default configuration it must be shorter than 8000 bytes.
If binary data or large amounts of information need to be communicated, it's best to put it in a database table and send the key of the record.