How to update database using flask and sqlalchemy?

Question

I have created a list of users using Postgres (users table) and connected it to my flask backend app, while trying to update the username using postman I have a not found error. Want to understand what is not working. Here is the code I am trying to run:

from flask import Blueprint, jsonify, abort, request
from ..models import User

bp = Blueprint('users', __name__, url_prefix='/users')

@bp.route('/<int:id>', methods=['PATCH','PUT'])
def update(id: int):
    u = User.query.get_or_404(id)
    try:
        if 'password' in request.json:
            if len(request.json['username']) < 3:
                return abort(404)
            u.username = request.json['username']
    
        # db.session.add(u)
        db.session.commit()
        return jsonify(u.serialize())
    except:
        # if something went wrong
        return jsonify(description='Something went wrong')