Attachment in Notify Action not recognized

Summary:

I want to add an File Attachment to the a Notify Action in an Integration. The attachment is coming as a file reference from a Write Stage File Response and is directly added in the attachment area of the notification.

Doing this I get an "Error occurred in fetching the attachment for Email".

In the Step following the notification I use the same file reference in a mapping for an ftp action / upload. And the file gets uploaded and contains data like expected.

As there is not much more in terms of error-message, is there some hint you can give me to get an idea what the problem is…?