如何解决创建新的Google云项目时“父id必须是数字”的问题

我试图通过以下命令行创建一个新的Google云项目:

$ gcloud projects create PROJECT_ID --folder=FOLDER_ID

但我错了:

ERROR: (gcloud.projects.create)
INVALID_ARGUMENT: field [parent] has issue [Parent id must be numeric.]
- '@type': type.googleapis.com/google.rpc.BadRequest
  fieldViolations:
  - description: Parent id must be numeric.
    field: parent
- '@type': type.googleapis.com/google.rpc.Help
  links:
  - url: https://cloud.google.com/resource-manager/reference/rest/v1/projects

看着 gcloud project create --help ,上面写着:

 --folder=FOLDER_ID
    ID for the folder to use as a parent