Since this is a GET request, the params need to be sent in the query string, not in the body like the create an order endpoint requires. The ? in the URL starts the query string.
Be sure to separate terms using <name>=<value> pairs in the query string, and use percent-encoding for all spaces or special characters like the playground on the right shows. You can type some spaces and special characters into the boxes below to see how they get encoded! If you need more information on GET vs POST requests, Mozilla's MDN has a nice summary.
Here are a few things to keep in mind while using this endpoint: