GCP :: gsutil unable to change ACL from CLI

Hi, I am giving following command to change the ACL for my bucket file, but receiving error. 
Is there some mistake?
command execute on bucket level only.

$ gsutil acl ch -u AllUsers:R gs://bucketabc_cli/myfile.pdf

CommandException: "acl" command does not support "file://" URLs. Did you mean to use a gs:// URL?