Terraform - Optional !?

terraform 你他媽的 Optional...

The following arguments are supported:

project - (Optional) The ID of the project in which the resource belongs.
If it is not provided, the project will be parsed from the identifier of the parent resource. If no project is provided
in the parent identifier and no project is specified, the provider project is used.

然後真的塞 project 進去, 就噴:

Error: Unsupported argument

An argument named "project" is not expected here.