Buy When the Price Drops

Your app can buy a product when its price falls under a limit. Crossmint does not watch prices. Your app starts a checkout on a schedule, and the spending cap stops the checkout while the total is too high. When the total is under the limit, an order intent that the user approved before pays for the order.

Prerequisites

Agent Checkouts integration — complete the quickstart and Pay for a Checkout.
A scheduler — a cron job or a queue in your backend that starts a checkout at fixed times.
Keys — a production server key with the Agent Checkouts scopes, and a client key with order-intents.create and order-intents.read.

Watch the Price and Buy

Ask the user to approve the limit

Create an order intent for the limit, for as long as you watch the price. The user approves it one time, in your app. Omit merchant: Agent Checkouts gives the merchant when it pays.

const expiresAt = new Date(Date.now() + 14 * 24 * 60 * 60 * 1000).toISOString();

const response = await fetch("https://www.crossmint.com/api/unstable/order-intents", {
    method: "POST",
    headers: {
        "Content-Type": "application/json",
        "X-API-KEY": "YOUR_CLIENT_API_KEY",
        Authorization: "Bearer YOUR_USER_JWT",
    },
    body: JSON.stringify({
        paymentMethodId: "YOUR_PAYMENT_METHOD_ID",
        amount: { value: "250.00", currency: "USD" },
        description: "Wireless headphones when the price is 250 USD or less",
        expiresAt,
    }),
});
if (!response.ok) {
    throw new Error(`Could not create order intent: ${response.status}`);
}
const { orderIntentId } = await response.json();

Verify the card rail if it is pending_verification, and store the orderIntentId. See Approve an Order Intent.

Start a checkout on a schedule

On each run of your scheduler, start a checkout with maxCost equal to the limit:

const response = await fetch("https://www.crossmint.com/api/unstable/agent-checkouts", {
    method: "POST",
    headers: {
        "Content-Type": "application/json",
        "X-API-KEY": process.env.CROSSMINT_SERVER_API_KEY!,
        "x-crossmint-user-id": "YOUR_USER_ID",
    },
    body: JSON.stringify({
        request: {
            startUrl: "https://shop.example.com/products/wireless-headphones",
            task: "Buy one pair of the wireless headphones in black. Use standard shipping and pay by card.",
        },
        buyerProfileId: "YOUR_BUYER_PROFILE_ID",
        constraints: { maxCost: { amount: "250.00", currency: "USD" } },
    }),
});
if (!response.ok) {
    throw new Error(`Could not start checkout: ${response.status}`);
}
const { runId } = await response.json();

A buyer profile gives the shipping address, so that the checkout does not stop to ask for it.

Act on the result

Follow the checkout and act on what happens. Run only one checkout at a time for this purchase: do not start the next scheduled checkout while one is still active.

What happens	What your app does
The checkout ends as `blocked` with `policy.max_cost_exceeded`	The total is still higher than the limit. Try again at the next run.
The checkout sends a payment request	The total is under the limit. Stop the schedule first, then answer with the stored `orderIntentId`. See Pay With an Order Intent.
The checkout ends as `succeeded`	Tell the user, and cancel the order intent, so that it cannot pay again.

Common Gotchas

Two checkouts can buy the product twice

Each checkout that reaches the payment step can use the order intent while its available amount covers the total. Run one checkout at a time, stop the schedule before you answer a payment request, and cancel the order intent after the purchase.

Each check costs a checkout

Crossmint bills each checkout that starts, also when it ends as blocked. Check at a reasonable interval, for example once a day.

The limit includes shipping and tax

maxCost applies to the total of the order. Tell the user that the limit includes shipping and tax.

The payment answer gets rail_unavailable

When the saved card has no network rail, the checkout uses the encrypted card, which needs the card’s security code. Crossmint keeps the code for a limited time. Ask the user to enter the CVC again, then answer the new payment request.

The order intent expired

The payment answer fails after the order intent’s expiresAt. Ask the user to approve a new order intent, or stop the schedule.

Next Steps

Check a Price Without Buying

Get the exact total of an order

Statuses, Results, and Errors

Handle every result of a checkout

Create a Checkout

Review the complete create request schema

Introduction

Agent Cards

Agent Wallets and Onramps

Agent Checkouts

API Reference

Prerequisites

Watch the Price and Buy

Common Gotchas

Next Steps

Check a Price Without Buying

Statuses, Results, and Errors

Create a Checkout

​Prerequisites

​Watch the Price and Buy

​Common Gotchas

​Next Steps

Check a Price Without Buying

Statuses, Results, and Errors

Create a Checkout

Prerequisites

Watch the Price and Buy

Common Gotchas

Next Steps