V6; Unless an "Accept" header is specified, Web Services will now return a JSON rather an XML Response

Under version 4 of Web Services, specifying the "Content-Type" header (to indicate whether parameters were being passed in XML or JSON format) was enough to tell Web Services the format to return the response in, e.g., the following will have returned an XML Response:

GET http://localhost:51149/Api/Ping/PingEx HTTP/1.1
Content-Type: text/xml
Host: localhost:51149

With version 6, and the move to ASP.NET Core, an "Accept" header must be specified if anything but the default response format (JSON) is required, e.g.:

GET http://localhost:51149/Api/Ping/PingEx HTTP/1.1
Content-Type: text/xml
Accept: text/xml
Host: localhost:51149