PostgreSQL is a very powerful database. One of the things that seems missing when moving from MySQL is the ability to simply create an enumeration. ENUM is nice when you have a programmatically-semantic set of values for a field.
In PostgreSQL, you have several choices. But one simple one is to create a Check expression, like follows. Skip the IS NULL part if you don’t want the field nullable.
ALTER TABLE "public"."CallCenter_Transfer" ADD CONSTRAINT "CallCenter_Transfer_TransferStatus" CHECK ( "TransferStatus" IS NULL OR "TransferStatus" = ANY(ARRAY['TransferComplete', 'TransferFailedNoAnswer', 'TransferFailedProspectLost']) )