Errror when trying to create a logical replication slot

Hi All,

We get the following error when trying to test creating a logical replication slot in Postgres version 11.9

>SELECT * FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
ERROR: cannot create logical replication slot in transaction that has performed writes

We are running the above command from psql and have tried issuing a rollback prior to running the command but still get the same error. 

We have the following settings enabled:

>show wal_level;
 wal_level
-----------
 logical

>show max_replication_slots;
 max_replication_slots
-----------------------
 25

Any suggestions on what may be causing the above error are appreciated. 

Regards,