declare @headers nvarchar(max), @url nvarchar(max), @payload nvarchar(max), @response nvarchar(max);
set @headers = json_object(
 'Accept': 'application/xml',
 'Content-Type': 'application/json',
 'BrokerProperties': '{"Label": "TestMessage", "SessionId": "Session1"}'
	);
set @payload = json_object('MessageId': 1);
select @headers, @payload;
set @url = 'https://{ServiceBusName}.servicebus.windows.net/{ServiceBusTopicName}/messages'
exec sp_invoke_external_rest_endpoint
 @url = @url,
 @method = 'POST',
 @headers = @headers,
 @payload = @payload,
 @credential = [https://{ServiceBusName}.servicebus.windows.net],
 @response = @response output
select cast(@response as xml)
go

<output>
 <response>
 <status>
 <http code="400" description="Bad Request" />
 </status>
 <headers>
 <header key="Date" value="2023年10月05日 13:32:20 GMT" />
 <header key="Transfer-Encoding" value="chunked" />
 <header key="Content-Type" value="application/xml; charset=utf-8" />
 <header key="Server" value="Microsoft-HTTPAPI/2.0" />
 <header key="Strict-Transport-Security" value="max-age=31536000" />
 </headers>
 </response>
 <result>
 <Error>
 <Code>400</Code>
 <Detail>The value '{\"Label\": \"TestMessage\", \"SessionId\": \"Session1\"}' of the HTTP header 'BrokerProperties' is invalid. TrackingId:1030e3ab-5a69-4414-b28e-73af5a76888d_G58, SystemTracker:***, Timestamp:2023年10月05日T13:32:19</Detail>
 </Error>
 </result>
</output>

<output>
 <response>
 <status>
 <http code="201" description="Created" />
 </status>
 <headers>
 <header key="Date" value="2023年10月05日 13:39:17 GMT" />
 <header key="Transfer-Encoding" value="chunked" />
 <header key="Content-Type" value="application/xml; charset=utf-8" />
 <header key="Server" value="Microsoft-HTTPAPI/2.0" />
 <header key="Strict-Transport-Security" value="max-age=31536000" />
 </headers>
 </response>
</output>

{"Accept":"application\/xml","Content-Type":"application\/json","BrokerProperties":"{\"Label\": \"TestMessage\", \"SessionId\": \"Session1\"}"}