server.py

#! /usr/bin/env python3.6
"""
Python 3.6 or newer required.
"""
import stripe

stripe.api_key = 'sk_test_sample_key'

from flask import Flask, jsonify

app = Flask(__name__, static_folder='public',
            static_url_path='', template_folder='public')

@app.route('/account_session', methods=['POST'])
def create_account_session():
    try:
        account_session = stripe.AccountSession.create(
          # We currently only support US custom accounts for onboarding
          # https://stripe.com/docs/connect/supported-embedded-components#account-onboarding for more info
          account="{{CONNECTED_ACCOUNT_ID}}",
          components={
            "account_onboarding": {
              "enabled": True
            },
          },
        )
        return jsonify({
          'client_secret': account_session.client_secret,
        })
    except Exception as e:
        print('An error occurred when calling the Stripe API to create an account session: ', e)
        return jsonify(error=str(e)), 500

if __name__ == '__main__':
    app.run(port=4242)