CREATE_REPLICATION_SLOT slot_name LOGICAL output_plugin
START_REPLICATION SLOT slot_name LOGICAL ...
are used to create, drop, and stream changes from a replication slot, respectively. These commands are only available over a replication connection; they cannot be used via SQL. See Section 51.3 for details on these commands.
The command pg_recvlogical can be used to control logical decoding over a streaming replication connection. (It uses these commands internally.)