Notification v7 uses WordPress' REST API to render the recipients field. You must ensure the
/notification endpoint is accessible and the API is accessible.
To debug the missing message (Carrier execution) please enable the Notification log in Notification > Settings > Debugging. All the executions will be caught there.
If the notification gets caught, you can inspect the details (ie. if the recipient is set correctly) and if they seem to be ok, check if your WordPress is sending the emails (SMTP is set correctly?) or it can connect to the API (depends on the selected Carrier).
If the notification is not there, you probably found a bug. Please report it on Github.
This error will most likely occur in tandem with:
Warning: ftp_nlist() expects parameter 1 to be resource, null given
To make sure the plugin works, please add the following to your
if (!defined('FS_METHOD')) define('FS_METHOD', 'direct');