Click to unsubscribe refers to localhost
https://github.com/SergeyMosin/Appointments/blob/7857af009eaa167723d97a69a1a91ec49291a742/lib/Backend/DavListener.php#L1538C32-L1539C29
While $cnl_lnk_url is build by overwrite.cli.url
// overwrite.cli.url must be set if $embed is not used
https://github.com/SergeyMosin/Appointments/blob/7857af009eaa167723d97a69a1a91ec49291a742/lib/Backend/DavListener.php#L339-L345
Reminder-Mails are never embedded, so it might happen that unsubscribe URLs are set to localhost.
A proper field to define the base url per appointment would be helpful.
In v2.1.5 additional checks have been added to only add the links if the overwrite.cli.url property contains a valid URL.
A proper field to define the base url per appointment would be helpful.
This is really up to admins to define the "base url" using overwrite.cli.url as per NC docs, and if it has not been defined, users can opt-out of spending the links by unchecking the Add actions links checkbox.