SQL 2012 Partitioning - Adding additional Partitions

I created some years ago a Partitioned table and now need to add additional partitions.  The problem I'm having is the ALTER statement for the Partition SCHEMA and FUNCTION.

I have attached the original query that created the existing partitions, schema and functions (CreatePart.sql) along with the update query (UpdatePart.sql).

This is the part that is not working:

ALTER PARTITION SCHEME COMPL_DTE__PS
NEXT USED TMS20181001

ALTER PARTITION SCHEME COMPL_DTE__PS
NEXT USED TMS20191001

ALTER PARTITION SCHEME COMPL_DTE__PS
NEXT USED TMS20201001


ALTER PARTITION FUNCTION COMPL_DTE_PF ()
SPLIT RANGE ( '20181001' )

ALTER PARTITION FUNCTION COMPL_DTE_PF ()
SPLIT RANGE ( '20191001' )

ALTER PARTITION FUNCTION COMPL_DTE_PF ()
SPLIT RANGE ( '20201001' )

This should be a simple task, but the syntax is driving me nuts.

Thank you.
CreatePart.sql
UpdatePart.sql