# What an order is

The one object every Kustom product shares — how amounts are written, why order lines must add up, what the two html_snippets are for and which fields the order carries from cart to refund.

An order is the cart as Kustom sees it, and it's the only object you ever really work with.
Checkout creates it, the customer pays it, Order Management captures and refunds it, Finance
settles it. The integration models differ in *where* the customer sees the order. The object is the same
throughout, so the rules below hold in every tab of these docs.

## What it carries

The fields group into four jobs. Everything else on the object is a detail of one of them, and
each job has one rule that bites.

<dl class="kd-fields not-content">
    <dt>Where, and in what money</dt>
    <dd class="kd-fields__names"><code>purchase_country</code> <code>purchase_currency</code> <code>locale</code></dd>
    <dd class="kd-fields__rule">Must match a market on your merchant account. <code>SE</code> / <code>SEK</code> / <code>en-SE</code> always works in the Playground.</dd>
    <dt>What is being bought</dt>
    <dd class="kd-fields__names"><code>order_lines[]</code> <code>order_amount</code> <code>order_tax_amount</code></dd>
    <dd class="kd-fields__rule">Every amount is in <strong>minor units</strong> — <code>25000</code> is 250.00 SEK — and the line totals must sum to the order totals exactly.</dd>
    <dt>Where Kustom calls you</dt>
    <dd class="kd-fields__names"><code>merchant_urls.terms</code> <code>.checkout</code> <code>.confirmation</code> <code>.push</code> <code>.validation</code></dd>
    <dd class="kd-fields__rule">Every URL Kustom calls — <code>confirmation</code>, <code>push</code>, <code>validation</code> — must be HTTPS. The first four are required, while <code>validation</code> and the shipping endpoints are not. The push URL is how you learn the order was placed even if the customer's browser never reaches your confirmation page.</dd>
    <dt>Who, and how</dt>
    <dd class="kd-fields__names"><code>billing_address</code> <code>shipping_address</code> <code>customer</code> <code>options</code> <code>merchant_reference1/2</code> <code>merchant_data</code></dd>
    <dd class="kd-fields__rule">Mostly filled in by the customer, not by you. Your own references are how you find the order again in your systems.</dd>
</dl>

## The two snippets

An order carries HTML twice, and both are yours to render.

1. **After you create it,** the response includes an `html_snippet`. Put it on your checkout
   page and its script loads the checkout iframe the customer pays in.
2. **After the customer pays,** reading the order back returns a second `html_snippet` — now a
   receipt — for your confirmation page.

Neither snippet is a URL you construct. Take them from the order as returned. The order's own
URL you do build, from the `order_id` you stored: `/checkout/v3/orders/{order_id}`.

## Why the totals are strict

Kustom doesn't correct a cart. It refuses one. `order_amount` must equal the sum of every
line's `total_amount`, and `order_tax_amount` the sum of every `total_tax_amount`, to the
minor unit. The reason is that the amount the customer sees, authorizes and is eventually
charged must be the same number all the way through, and a rounded line is the usual way
they drift apart. Compute line totals as `quantity × unit_price − total_discount_amount`,
derive tax from that and sum — the [live editor in the quickstart](/checkout/quickstart/)
checks this before it sends. A tiny rounding difference is tolerated rather than rejected, but
it exists to absorb the last minor unit of an awkward tax rate, not to license rounding: compute
the totals and there is nothing for it to absorb.

## One object, wherever it's paid

The same order is what a Checkout iframe, a Hosted Payment Page, Elements and an in-store
terminal all operate on. Choosing between them is a decision about rendering, not about the
API — [Integration models](/checkout/#integration-models) compares them.

## Related

- [What to send](/checkout/integrate/the-order/) — every field, live
- [Tax and order lines](/checkout/tax-and-order-lines/) — the arithmetic in full
- [Order lifecycle](/basics/order-lifecycle/) — what happens to the order after it's paid
- [Your own data on an order](/basics/conventions/merchant-data/) — `merchant_reference` and `merchant_data`