Update user in database on success from Stripe prebuilt checkout

Question

I am using Stripe's prebuilt checkout with react and firebase. The checkout process works fine and directs the user to the succes_url, but I would like to update a field under the user in the database as well. I don't understand how I can include a function that updates the DB that runs upon a successful checkout.

export const checkoutWithStripe = async(user) => {
    const checkoutSessionsRef = collection(db, 'users', user.uid, 'checkout_sessions');

    const singleCheckoutSessionRef = await addDoc(checkoutSessionsRef, {
        price: 'price_xyz',
        allow_promotion_codes: true,
        success_url: `${window.location.origin}/dashboard/app?success=true`,
        cancel_url: `${window.location.origin}/dashboard/app?canceled=true`
    });

    onSnapshot(singleCheckoutSessionRef, (snap) => {
        const { error, url: checkoutUrl } = snap.data();

        if (error) {
            console.error(`An checkout error occured: ${error.message}`);
        }
        if (checkoutUrl) {
            window.location.assign(checkoutUrl);
        }
        
    });

    // TODO: Update user type in firebase from free to starter on successful checkout
};

Thankful for any help.

Update:

I solved it, in 2 parts.

1. In Stripe I created a new webhook that points to a exported firebase function (2) that fires when "checkout.session.completed" is fired.

2. In Firebase i created a function that listens for the "checkout.session.completed" event and then calls a function that updates the DB based on the user email that I get from the Stripe event.

This is the Firebase function that listens to the event:

/**
 * A webhook handler function for the relevant Stripe events.
 */
exports.updateCustomer = functions.https.onRequest((req, resp) => {

    functions.logger.log("updateCustomer body", req);

    const relevantEvents = new Set([
        'checkout.session.completed'
    ]);
    let event;

    // Instead of getting the `Stripe.Event`
    // object directly from `req.body`,
    // use the Stripe webhooks API to make sure
    // this webhook call came from a trusted source
    try {
        event = stripe.webhooks.constructEvent(
            req.rawBody,
            req.headers['stripe-signature'],
            endpointSecret
        );
    } catch (error) {
        functions.logger.log(`Webhook Error: Invalid Secret`);
        resp.status(401).send('Webhook Error: Invalid Secret');
        return;
    }

    functions.logger.log("updateCustomer", event.type);

    if (relevantEvents.has(event.type)) {
        // logs.startWebhookEventProcessing(event.id, event.type);
        try {
            switch (event.type) {
                case 'checkout.session.completed':
                    const session = event.data.object;
                    functions.logger.log("checkout.session.completed:", session);
                    updatePlan(session.customer_details.email);
                    break;
                default:
                    functions.logger.log(`Unhandled event type ${event.type}`);
            }
        } catch (error) {
            functions.logger.log(`Unhandled event error ${event.type}`);
            resp.json({
                error: 'Webhook handler failed. View function logs in Firebase.',
            });
            return;
        }
    }

    // Return a response to Stripe to acknowledge receipt of the event.
    resp.json({ received: true });
});

Answer 1

If you need to run some code when the Checkout Session is successful, then you should use Stripe webhooks and listen to the checkout.session.completed event. This is covered in the Stripe documentation.