The receiver MUST begin the revocation list update procedure by sending a POST request to the URL that the receiver intends to play or is currently playing. The entity-body of the POST request MUST contain a revocation list request message.

The POST request MUST include a "Content-Type: application/vnd.ms-wmdrm-extended-operation-request" header to indicate that the body of the POST request contains a revocation list request message.

Unlike the registration request and registration response messages, the revocation list request and revocation list response messages MUST NOT be encoded or decoded in Base64 [RFC3548].

When the receiver receives the response to the POST request, it MUST verify that the response indicates that the request succeeded. The receiver MUST also verify that the response includes the "Content-Type: application/vnd.ms-wmdrm-extended-operation-response" header. The presence of this header indicates that the entity-body of the response contains a revocation list response message.