Flask SQLAlchemy Heroku error: duplicate key value violates unique constraint

I have a Flask application which uses SQLAlchemy to store its data

I have a model AdminModel as shown below:

admin.py

class AdminModel(database.db.Model):
__tablename__ = "admins"

id = database.db.Column(database.db.Integer, primary_key=True)
email = database.db.Column(database.db.String(80))
username = database.db.Column(database.db.String(80))
password = database.db.Column(database.db.String(80))

def __init__(self, email, username, password):
    self.email = email
    self.username = username
    self.password = password

...

def insert(self):
    admin = self.find_by_username(self.username)
    if admin is None:
        # Hash the password
        self.password = utils.hash(self.password)
        # Add to DB
        database.db.session.add(self)
        database.db.session.commit()
        return True

    return False

init.py:

def create_default_admin():
    keys = settings.TwitterSettings.get_instance().super_admin # returns ["adminemail", "adminusername", "adminpassword"]
    admin = admin_mod.AdminModel(keys[0], keys[1], keys[2])
    admin.insert()


def create_app():
    # Create a Flask Application
    app = Flask(
        __name__,
        template_folder="templates",
        static_folder="static",
        instance_relative_config=True,
    )

    # Register blueprints
    app.register_blueprint(admin.admin, url_prefix="/admin")
    app.register_blueprint(live.live, url_prefix="/web")
    app.register_blueprint(api.api_bp, url_prefix="/api")

    # Flask configurations
    # app.config["SQLALCHEMY_DATABASE_URI"] = f"sqlite:///databases/fortweets.db"
    app.config["SQLALCHEMY_DATABASE_URI"] = os.environ.get(
        "DATABASE_URL", f"sqlite:///databases/fortweets.db"
    )
    app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False
    app.config["PROPAGATE_EXCEPTIONS"] = True
    app.secret_key = settings.TwitterSettings.get_instance().jwt_secret_key

    # # SQLAlchemy configurations
    # database.db.app = app
    # database.db.init_app(app)
    # database.db.create_all()

    database.db.app = app
    database.db.init_app(app)
    database.db.create_all()

    return app


# Create the app
app = create_app()

# JWT Configurations
jwt = JWTManager(app)

# Socket IO
socketio = SocketIO(app, cors_allowed_origins="*")

# Creates default admins and insert in db
create_default_admin()

...


# Start the app
if __name__ == "__main__":
    socketio.run(app, host="0.0.0.0")

When i run this app locally on my laptop, it works fine.

When i run it on Heroku (With postgres database add-on in Heroku) i get the following error in logs:

2020-12-04T11:04:57.005331+00:00 app[web.1]: sqlalchemy.exc.IntegrityError: 

(psycopg2.errors.UniqueViolation) duplicate key value violates unique constraint "pg_type_typname_nsp_index"
2020-12-04T11:04:57.005331+00:00 app[web.1]: DETAIL:  Key (typname, typnamespace)=(admins_id_seq, 2200) already exists.
2020-12-04T11:04:57.005331+00:00 app[web.1]:
2020-12-04T11:04:57.005331+00:00 app[web.1]: [SQL:
2020-12-04T11:04:57.005332+00:00 app[web.1]: CREATE TABLE admins (
2020-12-04T11:04:57.005332+00:00 app[web.1]: id SERIAL NOT NULL,
2020-12-04T11:04:57.005332+00:00 app[web.1]: email VARCHAR(80),
2020-12-04T11:04:57.005332+00:00 app[web.1]: username VARCHAR(80),
2020-12-04T11:04:57.005333+00:00 app[web.1]: password VARCHAR(80),
2020-12-04T11:04:57.005333+00:00 app[web.1]: PRIMARY KEY (id)
2020-12-04T11:04:57.005333+00:00 app[web.1]: )
2020-12-04T11:04:57.005334+00:00 app[web.1]:
2020-12-04T11:04:57.005334+00:00 app[web.1]: ]

Can someone tell me what I'm doing wrong please

Why is it working locally with sqlite3 but not Heroku Postgresql?