Just throws a 400 bad request
You can probably configure your webclient by adding a custom DefaultUriBuilderFactory with EncodingModel NONE but that probably creates other problems on the road.
You can try a different way
In queryParam value just use a variable name, e.g. {selector} and pass the json contents in the build method
That seemed to have worked, but run into an issue with deserialization. I can try and work through that
Actually, just kidding that did not work the way I thought it would.