Drop all connections to a Postgres database so you can drop the DB. Make sure you are not currently connected to the database that you wish to drop!

drop_all_connections.sql

SELECT pg_terminate_backend(pg_stat_activity.pid)
FROM pg_stat_activity
WHERE pg_stat_activity.datname = 'TARGET_DB' -- ← change this to your DB
  AND pid <> pg_backend_pid();