Changes to Do a partial update of an existing customer's bill messages

request body became required

removed the media type application/json for the response with the status 200

removed the media type application/json for the response with the status 500

removed the media type text/html for the response with the status 200

removed the media type text/html for the response with the status 500

removed the media type text/json for the response with the status 200

removed the media type text/json for the response with the status 500