DICOM PS3.18 2016a - Web Services
6.9.5.3.2 Response Headers

If the User-Agent specifies a Procedure Step State (0074,1000) attribute with a value of "CANCELED" and the UPS Instance is already in that state, the response message shall include the following HTTP/1.1 Warning header field:

If the User-Agent specifies a Procedure Step State (0074,1000) attribute with a value of "COMPLETED" and the UPS Instance is already in that state, the response message shall include the following HTTP/1.1 Warning header field:

If the request was rejected with an HTTP/1.1 409 status code, the response message shall include one of following messages in the HTTP/1.1 Warning header field describing the nature of the conflict:

DICOM PS3.18 2016a - Web Services