This service is deployed as a lambda function on Netlify. You can reach it at https://gsx2json.mappr.dev/.netlify/functions/app
A complete query will look like this https://gsx2json.mappr.dev/.netlify/functions/app/api?id=1hOIkY21AR0RwzJXxBBDaBfY3eUX0HkXtIIE0Cmkadug&sheet=1&columns=false
Check detailed usage here: https://github.com/55sketch/gsx2json