Related Questions:
Why don't all of my merge fields work in my email templates when I use them with Workflows?
Can I send a document link in an email template using a Workflow?
Answer:
Some Merge Fields will not work in your Email Templates when sending them via a Workflow.
The following Merge Fields in these categories will not work:
Invoice
Document
The reason for this is that Workflow Email Actions do not allow you to assign an Invoice or a Document and without having one of these assigned to an Email the Merge Fields will not know where to get the data from.
When using Email Templates with Workflows you will need to select Templates that do not use these Merge Fields. If the Template does include a Merge Field from one of these categories, it will simply be blank in the email.
Events - Event Merge Fields will work when used with Workflows but be aware that the Workflow will automatically choose the Event with the earliest start date/time and you cannot change this choice. If your Events have the same start dates/times then it will choose a random Event for the email.