tortoise.exceptions.ConfigurationError: Unknown DB scheme: postgresql error

I'm learning tortoise and am trying to configure Postgres with register_tortoise looking like below:

register_tortoise(
    app,
    db_url="postgresql://postgres:password@localhost:5432/testdb",
    modules={'models': ['db.models.users']},
    generate_schemas=True,
    add_exception_handlers=True
)

But I get this error

tortoise.exceptions.ConfigurationError: Unknown DB scheme: postgresql

ERROR:    Application startup failed. Exiting.

Could someone help me figure out the error?