The 10. User ID variable works when it is a direct message to one person, as does the User ID that doesn’t vary. How do I send to multiple people? Is the formatting here incorrect?
Hey Annabel,
despite what the name says, Direct message to multiple people doesn’t actually send individual messages to a list of people. I don’t know why they called it that.
If you toggle the Map off you will possibly see channels that fall under this category and can be mapped there. In Slack it self you can create a direct message channel with several people inside, this is what this options can send messages to.
Hey Stoyan, thank you for your helpful response 
This is an example of the channels it shows as a dropdown - is there a way to export this list so I can somehow map it?
Essentially then there isn’t a way to create a small group dm (i.e. me, the variable user and the static user) each time?
You can use the List Channels module to find existing ones, but I’m not sure how to create new channels of this type via the API. As far as I can tell, you can try and create a standard channel with these specific people inside and message them there.