Response type "pass through" works as expected, but when I changed it to "XML" only GET requests works

Question

I have a MPG that, until now, the request and response were defined as "pass through", but now I want to ensure that the request is XML.

I defined the Request Type as "XML", and now only GET requests make it through to the server.

In the probe I see, what seems to me, a perfectly valid XML, but after the implied filter it drops it with error 'rejected'.

I'm sending the XML, to test, via curl as such curl -X POST -d '<note>value</note>' -H 'Content-Type: application/xml' http://1.2.3.4:5678