That got it closer, but I'm now getting EHttpException with message 'Query not provided'.
I have moved the query into the unit and updated the pastebin. With the debugger, I can see that the IGraphQLHttpRequest.GetContent has the query text and is called before I get the error.
I checked the schema using the Bookshelf demo with some modified names and that worked ok.
Are the following assumptions correct ?
the url does not have to be real or match anything specific
the Content-Type I have tried with application/octet-stream, text/html and text/plain
the Method is POST
the GetContent is 8 bit ascii (ie an ansistring is ok to be moved into the result)