How to define event description for internal invoice format

Summary:

For internal customer billing we create events. The event description needs to appear on the internal customer invoice. When I define the invoice format for internal event billing it seems I can only have the grouping option by contract line. But that grouping option doesn't provide me with the Event description in the invoice details section. Is there an option which allows to select the event description in the invoice details section of the invoice format?

Content (please ensure you mask any confidential information):

Version (include the version you are using, if applicable):

Code Snippet (add any code snippets that support your topic, if applicable):