My curl HTTP API call always creates an empty row

You are probably putting your request parameters as GET query strings.

Ragic's HTTP API is RESTful, meaning that a GET command will retrieve data, and a POST command will insert/update data. The -d or --data parameter you used will make the request a POST request. You need a GET request to retrieve data. You can see https://curl.haxx.se/docs/manpage.html for more details on the parameters of curl.