flask command Error: No such command ["create_db"]

The issue was that the command.py module was not recognized by the app. The solution, I tried is to initiate a blueprint in the commands module and then in the __init__.py module where I initiated the app instance, I registered the corresponding Blueprint with it. So, the updated commands.py-

from FlaskUserAuthentication import db
from flask import Blueprint
from FlaskUserAuthentication.API.db_models import Group, Member, Project, Milestone

@cmd = Blueprint('db', __name__) #created a Blueprint for this module

@cmd.cli.command('create_db') #rather than generating the cli command with app,
def createDatabase():         # used the blueprint, cmd
    db.create_all()
    print('***** Datebase created ****')

and the updated __init__.py module,

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)

app.config['SECRET_KEY'] = 'justasamplekey'
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///database.db'
db = SQLAlchemy(app)

from FlaskUserAuthentication.API.routes import api
from FlaskUserAuthentication.Site.routes import site
from FlaskUserAuthentication.commands import cmd

app.register_blueprint(api)
app.register_blueprint(site)
app.register_blueprint(cmd) # registered the command module as blueprint

Now set the environment variable and development server with (in the terminal) -

export FLASK_APP=FlaskUserAuthentication/__init__.py
export FLASK_DEBUG=1

After that use the flask command like-

flask db create_db

P.S.: now because of the Blueprint rather than flask create_db, the command will be

flask db create_db

I needed to realise the root of the issue and for that I thank the author of the post-

Where should I implement flask custom commands (cli)

and the author, @emont01 for his response to the post.