Trying to run a website using flask and ngrok on google colab and when i return render_template('layout.html'), the site have error

Question

Basically, when i return "Hello", the website load fine but if i return render_templat('layout.html'), the site has errorImage of the error Here's the folder that houses these filesFolder Here's the code

from flask import Flask, render_template
from flask_ngrok import run_with_ngrok
!ngrok authtoken '--token--'
# Webserver gateway interface
app = Flask(__name__)
run_with_ngrok(app)
@app.route('/')
def index():
    return render_template('layout.html')
if __name__ == "__main__":
    app.run()

i don't really understand it works so i haven't try anything. Hope anyone can help me