curl -u user:password -H 'Accept: application/json' -X GET
If so, then we know the 406 HTTP status means that if a web server detects that the data it wants to return is not acceptable to the client, it returns a header containing the 406 error code.
The client can define the characteristics of the data it will accept back from the web server by using the accept headers.
In this case you declare that you would like to accept application/json:
Request.AddHeader("Accept", "application/json");
I believe Graylog accepts this header already, unless something has changed.
Judging from Graylogs API browser the response content type is in application/json.
Can you execute the same search on the browser? System/Nodes → API browser.
This is unusual issue, since the request are enabled for application/json already. But the CSV export produces output with the MIME type text/csv, which you have to send in your HTTP Accept request header that’s the only one I know of. Can you show exactly what you executing? minus the personal information.