Changes to Trigger Broadcast

added the new optional request property precompute

added the new optional request property cancellation_key

removed the media type application/json for the response with the status 202

removed the media type application/json for the response with the status 400

the trigger_at request property format was generalized from date to date-time

added the media type text/plain for the response with the status 202

added the media type text/plain for the response with the status 400

added the pattern ^[a-z0-9_-]+$ to the request property list_id

api path removed without deprecation

endpoint added