Hi 
I have been poking around with the V2 API, and are currently having issues with the Watcher part.
The Jira Cloud platform REST API (atlassian.com)
If i execute this code, then the account that have logged in are added as a watcher - just as described in the documentation:
But i want to specify another user, based on that users AccountID - so i came up with this:
I have even tried with just just having body as a string - $body = "123-456-789"
Both of these give an error 400.
How should the body look, for this to work?