Postgres Logical replication setup error: The requested flag is either misspelled or unsupported

[rmyung_mh]

I am trying to setup Logical Replication following https://cloud.google.com/sql/docs/postgres/replication/configure-logical-replication 

When I try to enable the flags "cloudsql.enable_pglogical=on" or "cloudsql.logical_decoding=on" I get the errors 

ERROR: (gcloud.sql.instances.patch) HTTPError 404: The requested flag is either misspelled or unsupported by Cloud SQL. This command is authenticated as XX@XX.com which is the active account specified by the [core/account] property.
Failed to set cloudsql.logical_decoding on primary instance: XX
ERROR: (gcloud.sql.instances.patch) HTTPError 404: The requested flag is either misspelled or unsupported by Cloud SQL. This command is authenticated as XX@XX.com which is the active account specified by the [core/account] property.
Failed to set cloudsql.enable_pglogical on primary instance: XX

I was able to set the flags via the console, but want to be able to do this in a script.