Email buyers their product and receipt after a Stripe payment

import base64
from email.message import EmailMessage
from google.oauth2.credentials import Credentials
from googleapiclient.discovery import build
import stripe
from clickruntime import on_event, credentials, verify, state

LINKS = {"prod_Templates": "https://files.example.com/templates.zip", "prod_Course": "https://learn.example.com/start"}

def send(to, subject, text):
    msg = EmailMessage()
    msg["To"], msg["Subject"] = to, subject
    msg.set_content(text)
    gmail = build("gmail", "v1", credentials=Credentials(credentials.connection("google", "work")), cache_discovery=False)
    gmail.users().messages().send(userId="me", body={"raw": base64.urlsafe_b64encode(msg.as_bytes()).decode()}).execute()

@on_event
def handle(event):
    if not verify.stripe(event.body, event.header("Stripe-Signature"), credentials.secret("STRIPE_WEBHOOK_SECRET")):
        return {"ignored": "bad signature"}
    session = event.json["data"]["object"]
    if state.get(f"done:{session['id']}"):
        return {"duplicate": True}
    stripe.api_key = credentials.secret("STRIPE_API_KEY")
    items = stripe.checkout.Session.list_line_items(session["id"], expand=["data.price.product"]).data
    lines = [f"{i.description}: {LINKS.get(i.price.product.id, 'we will send this to you shortly')}" for i in items]
    total = f"{session['amount_total'] / 100:,.2f} {session['currency'].upper()}"
    send(session["customer_details"]["email"], "Your purchase", "Thanks for your order.\n\n" + "\n".join(lines) + f"\n\nReceipt: {total} paid.")
    state.set(f"done:{session['id']}", True)
    return {"items": len(items)}