How can we change the Blocked field, the Blocker and the ScheduleState of a user story?
The UserStory's endpoint is called: "HierarchicalRequirement". You can see it defined in the WSAPI Object Model (left bar on that page).
Make certain you include the ZSESSIONID with your api-key as at http header variable for any WSAPI request. In order to post updates to any artifacts (User Stories included) you shall find their ObjectID first, then call their endpoint/objectid as in:
Here is a JSON example of how to post changes to the Blocked, BlockedReason and ScheduleState fields.
Here is the result: