sqlalchemy.exc.OperationalError: (sqlite3.OperationalError) attempt to write a readonly database

I have an sqlite database using flask_login. The setup works locally, but not on the actual VPS (can still login, but unable to add new users to db)

UPDATE:

after removing the try-catch block I got the actual error:

sqlalchemy.exc.OperationalError: (sqlite3.OperationalError) attempt to write a readonly database

I've run the following permissioning, but it still does not work:

chmod 666 users.db
sudo chown www-data /var/www/mywebsite/db/
sudo chown -R www-data: /var/www/mywebsite/db/

the output of getfacl users.db permissions check is:

# file: users.db
# owner: www-data
# group: www-data
user::rw-
group::rw-
other::rw-

UPDATE 2:

I ran these 4 commands and it worked:

sudo chown -R www-data:www-data /var/www/mywebsite/db/
sudo chmod -R u+w /var/www/mywebsite/db/

sudo chmod 666 users.db
sudo chmod 777 db

I think the 777 permissions is a security risk though - but it didn't work with 666. How do I set it without compromising security?

config.py
import configparser
from sqlalchemy import create_engine

config = configparser.ConfigParser()
config.read('config.txt')

engine = create_engine(config.get('database', 'con'))

config.txt

[database]
con = sqlite:///users.db

failing code in auth.py

def add_user(first, last, password, email, engine):
    table = user_table()
    hashed_password = generate_password_hash(password, method="sha256")

    values = dict(first=first, last=last, email=email, password=hashed_password)
    statement = table.insert().values(**values)

    conn = engine.connect() ## cannot connect here
    conn.execute(statement)
    conn.close()
    return True