What is "file_id"?

[rysi3k]

Hello,
in documentation there is endpoint "GET /org/{org_id}/workspace/{workspace_id}/file/{file_id}". But nowhere is described what "file_id" is.
I want to get url to uploaded file. As i know, i can do this by fetching note with type=RESOURCE, but there is no url to file. How can i do this?
I tried to use resource_id as file_id but I recevied 401 error.

Thanks in advance.
Regards.