Cannot create secret key in flask; returns “name 'session' is not defined”

Im attempting to create a website in flask. To do that, I need use sessions and therefore I am required to use a secret key. I did all of that, and yet it still returns a long error log with nameerror: name ‘session’ is not defined at then end

I tried everything and moved the thing that sets the secret key everywhere, but it always had the same issue. Here is my code currently:

from flask import Flask
import os
app = Flask(__name__)
app.secret_key = os.urandom(24)

usernumber = 0

@app.route('/')
def homepage():
    global usernumber
    session['usernumber'] = usernumber
    usernumber = usernumber + 1
    Usernumberstring = session['usernumber']
    return f"Welcome {Usernumberstring}"

if __name__ == '__main__':
    app.run(use_reloader=True, debug=False, host="0.0.0.0")