Look at the JavaScript console.

XMLHttpRequest cannot load http://127.0.0.1:5000/api/v2/item/556db39fa114604bac0757d1.
No 'Access-Control-Allow-Origin' header is present on the requested resource.
Origin 'null' is therefore not allowed access. The response had HTTP status code 404.
OPTIONS http://127.0.0.1:5000/api/v2/item/556db39fa114604bac0757d1

The command-line console of Dancer.

looking for options /api/v2/item/556db39fa114604bac0757d1