Error undefined method `file_format' for nil:NilClass on new REST API

I just created a new REST API, without customizing anything but the endpoint URL. However, I’m getting the error {“error”:“undefined method `file_format’ for nil:NilClass”}

I already set a unique URL, and I’m sending the key but still it doesn’t work. The URL is https://my.api.mockaroo.com/users/unique.json?key=12345

The handler script is the default one:

schema "Users"
generate 2

Why it doesn’t work?

EDIT: Forget it. I didn’t know I had to create a Schema in order to use it in the REST API. SOLVED.