Apparently everyone jumped in while I was putting together a longer response
Just in case it does help, here’s what I had.
Here’s an example Drafts action and Workflow.
The workflow just wraps the content it is given with two lines of three hyphens.
The Drafts action calls the Workflow twice.
The first call is using the x-callback URL step where it then uses the callback based template tag to insert the text returned into the draft at the current cursor position.
The second call does the same, just using the preferred Workflow step. This returns the workflow based template tag and the insertion is as per the first round.
I included both in case you wanted to see how you might use it for something that isn’t Workflow of or Shortcuts which Drafts 5 has (/will have) steps for,
Note that Workflow returns the result in
return as specified in the Workflow documentation. Drafts is then prefixing that with an action step identifier to make it available as a template both for callbacks and for workflows.