set-body policy to set the message body for incoming and outgoing requests. To access the message body you can use the context.request.body property or the context.response.body, depending on whether the policy is in the inbound or outbound section.context.request.Body or context.response.Body, the original message body is lost and must be set by returning the body back in the expression. To preserve the body content, set the preserveContent parameter to true when accessing the message. If preserveContent is set to true and a different body is returned by the expression, the returned body is used.preserveContent to true because you are explicitly supplying the new body contents. Preserving the content of a response in the inbound pipeline doesn't make sense because there is no response yet. Preserving the content of a request in the outbound pipeline doesn't make sense because the request has already been sent to the backend at this point. If this policy is used when there is no message body, for example in an inbound GET, an exception is thrown.