permission denied to create extension "uuid-ossp"

ALTER USER root WITH SUPERUSER if the user of the database was root but in case it wasn't, you need to run psql as a superuser first before you run this command so you run

sudo -u postgres psql postgres

then

ALTER USER mydb_user WITH SUPERUSER;

Figured it out, I need to postegresql and change the root role to superuser:

$psql

ALTER USER root WITH SUPERUSER;