[Python] Trying to build a Flask webpage which stores username dynamically

I am trying to build a Flask website in Python. The idea is that initially, the user will go to a login page, type their name into the input bar, and then the Home page will pop up saying 'welcome <username> '. Here is my code:

from flask import Flask, render_template, request, url_for, redirect
app = Flask(__name__)


@app.route('/home/<username>')
def home_page(username):
message = f"Welcome {username}"
return message
#return render_template('home.html')


# home route that returns below text when root url is accessed
@app.route('/', methods=['POST', 'GET'])
def login_page():
if request.method == 'POST':
username = request.form['username']
return redirect(url_for('home_page', name=username))
return render_template('login.html')


@app.route('/contact')
def contact_page():
return render_template('contact.html')


if __name__ == '__main__':
app.run(debug=True)


Here is the html script. It's very simple:

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Login</title>
</head>
<body>
<form
action='http://127.0.0.1:5000/'
method='POST' >

<h1> Welcome to my Art! </h1>
<br>
<h2> First you must login... </h2>
<label> Please enter your name: </label>
<div>
<input type="text" name="username" />
</div>

<div>
<br>
<button type="submit" name='submit'> Submit </button>
</div>

</form>

</body>
</html>


However, when I type my name into the webpage and press the Submit button, this error message comes up:

error message

Could someone please help me with this?

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