Flask app secret key is not loading with Gunicorn

When I try to run my Flask using gunicorn -w 3 wsgi:app, and visit the page via the ip address, then I receive the following error: RuntimeError: A secret key is required to use CSRF. in the terminal.

I am not sure what is causing this issue because: I have set a secret key in .env and I have confirmation that it is being loaded by Flask because when I run the app using flask run --host=0.0.0.0, then the codeprint(app.config['SECRET_KEY']) prints the secret key to the terminal.
I imagine this is something to do with Gunicorn needing a different code for it to load the secret key.

My Flask app is structured like so:
-denise
--configmodule.py
--__init__.py
--site.db
--models.py
--main
--static
--template

-migrations
-venv
-wsgi.py
-.env

I don't have much experience setting up servers, here are the code from the relevant files:

__init__.py file:

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from denise.configmodule import Config
from flask_bcrypt import Bcrypt
from flask_login import LoginManager
from flask_mail import Mail
from flask_migrate import Migrate
from flask_wtf.csrf import CSRFProtect

db = SQLAlchemy()
bcrypt = Bcrypt()
login_manager = LoginManager()
mail = Mail()
csrf = CSRFProtect()

def create_app():
    app = Flask(__name__)
    app.config.from_object(Config)
    csrf.init_app(app)
    migrate = Migrate(app,db)
    db.init_app(app)
    bcrypt.init_app(app)
    login_manager.init_app(app)
    mail.init_app(app)
    print('SECRET_KEY')
    print(app.config['SECRET_KEY'])
    print('SECRET_KEY')

    #with app.app_context()
    from .main.routes import main

    app.register_blueprint(main)
    return app                                

configmodule.py file:

from os import environ, path
from dotenv import load_dotenv

basedir = path.abspath(path.dirname(__file__))
load_dotenv(path.join(basedir, '.env'))

class Config(object):
    DEBUG=True
    SECRET_KEY=environ.get('SECRET_KEY')
    SQLALCHEMY_DATABASE_URI='sqlite:///site.db'
    ENV='development'
    MAIL_SERVER = 'smtp.googlemail.com'
    MAIL_PORT = 587
    MAIL_USE_TLS = True
    MAIL_USERNAME = environ.get('EMAIL_USER')
    MAIL_PASSWORD = environ.get('EMAIL_PASS')
    MAIL_DEFAULT_SENDER = environ.get('EMAIL_DEFAULT_SENDER')
    MAIL_MAX_EMAILS = 5
    RECAPTCHA_PUBLIC_KEY = environ.get('RECAPTCHA_PUBLIC')
    RECAPTCHA_PRIVATE_KEY = environ.get('RECAPTCHA_PRIVATE')                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       

Wsgi.py file:

from denise import create_app
from dotenv import load_dotenv

load_dotenv('.env')

app = create_app()

if __name__ == "__main__":
    app.run()

.env file:

SECRET_KEY='hiiii17011b97b7ed4aeb9ae7f75a0b66a006c8efd4ab0759e5d2'
EMAIL_USER='email@email.email'
EMAIL_DEFAULT_SENDER='email@email.email'
EMAIL_PASS='password'
RECAPTCHA_PUBLIC='randomstringofletter'
RECAPTCHA_PRIVATE='lalalalalal'                                                                  

I have tried a few tutorials on deploying Flask apps to production by Corey Schafer and Pretty Printed. I guess I have missed something somewhere.

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