1. Initialize the Stripe webhook

You first need a Polyfire project. You can create one here.
Go to Auth > Payments on your Polyfire dashboard.
Copy the webhook URL for one of the next steps.

2. Configure User Rate Limits

Free User Rate Limit :
Set a dollar threshold for free app usage under Free User Rate Limit.
Premium User Rate Limit :
Assign a higher dollar limit for premium users in the Premium User Rate Limit.
Developer Rate Limit Testing:
To test rate limits, toggle Dev has rate limit? to 'On' in development.
Adjust or disable this in production.
Now save your settings by clicking on the "Save" button.

2. Add the webhook on the Stripe dashboard

Add the generated webhook here on Stripe .
Configure the webhook to be sent on all events (You can also select manually theses events: customer.created, customer.updated, checkout.session.completed, customer.subscription.created, customer.subscription.updated and customer.subscription.deleted)

3. Create a payment link

Create a new Stripe payment link here on your Stripe dashboard.
In the product field, select Add new product, give it the name, image, description and price you want. Set the payment to Recurring and select Monthly in billing period.
In the After payment tab, choose Don't show confirmation page and set the address of your app.
NOTE: for localhost, use http://127.0.0.1, you will need this address instead of http://localhost in your tests to stay connected after the payment.
Create the link and copy it.

4. Add the paywall to your app

For this part, I am going to use the chat we made in this tutorial: Making ChatGPT

We create a component that will be displayed instead of the chat if this user didn't pay yet. Don't forget to replace <YOUR_STRIPE_PAYMENT_LINK> by your payment link.

Polyfire uses the userID as the identifier to know which user paid a subscription, this is why we use the client_reference_id query parameter.

function Paywall({ userId }: { userId: string }) {
    return (
    <div className="flex flex-col justify-center items-center h-full py-2">
        <a className="cursor-pointer bg-black text-white ml-2 p-2 px-5 font-mono" href={`<YOUR_STRIPE_PAYMENT_LINK>?client_reference_id=${userId}`}>
            Access this application for only 420.69$/month
        </a>
    </div>
    );
}

We can then modify the App component to get the userId and add the paywall when the rate limit has been reached - which should be right away in this case since the rate limit is 0.

function App() {
  const polyfire = usePolyfire();

  const { login, status, user } = polyfire.auth;
  const { getAuthID, usage } = user;

  const { Chat } = polyfire.utils;


  const [chat, setChat] = useState<ChatType>();
  const [paywall, setPaywall] = useState(false);
  const [userId, setUserId] = useState<string>();
  const [messages, setMessages] = useState<
    { is_user_message: boolean; content: string }[]
  >([]);

  useEffect(() => {
    if (status === "authenticated") {
      const updateUsage = async () => {
        const userId = await getAuthID();
        setUserId(userId);

        const userUsage = await usage();
        if (userUsage.rateLimit === undefined || userUsage.rateLimit === null) {
          setPaywall(false);
        } else {
          setPaywall(userUsage.rateLimit <= userUsage.usage);
        }

        setChat(new Chat());
      };

      updateUsage();
    }
  }, [status]);

  if (status === "unauthenticated") {
    return (
      <button onClick={() => login({ provider: "github" })}>
        Login with Github
      </button>
    );
  }

  if (chat && !paywall) {
    return (
      <ChatBox
        messages={messages}
        onMessage={async (message: string) => {
          await chat.sendMessage(message);
          setMessages((await chat.getMessages()).reverse());
        }}
      />
    );
  }

  if (paywall && userId && status !== "loading") {
    return <Paywall userId={userId} />;
  }

  return <div>Loading...</div>;
}