The uuid-ossp module provides functions to generate universally unique identifiers (UUIDs) using one of several standard algorithms. There are also functions to produce certain special UUID constants.

To install uuid extension

CREATE EXTENSION IF NOT EXISTS "uuid-ossp";

https://stackoverflow.com/questions/22446478/extension-exists-but-uuid-generate-v4-fails

https://www.postgresql.org/docs/devel/static/uuid-ossp.html