To overview Gateway service description clik on to the Gateway which reside in the middle of the map. By that dialog screen you can access to the Protocol Transformation property of each method in that service.
From that dialog screen;
can be changed.
Also you can display a sample message by clicking to the button at the bottom.
If you want it is possible to build your own REST message on APINIZER. For this click to the Build Message button.
You can transform your REST messages from this page.
You can specify the part of the JSON message to be in array notation even if the object has only one element. Specify the path starting from the base element and use # by each sub group names. For instance a path which is specified as Response#Information#Address conveys that Address element is an array.
To apply all the changes please re-deploy the Gateway after the operation.