# Checkout Callback API

Callbacks Kustom makes to merchant URLs.

## Operations

- `POST /merchant_urls.address_update` — [Address update](/api/checkout/callbacks/update-address.md)
- `POST /merchant_urls.country_change` — [Country change](/api/checkout/callbacks/country-change.md)
- `POST /merchant_urls.shipping_option_update` — [Shipping option update](/api/checkout/callbacks/update-shipping-option.md)
- `POST /merchant_urls.validation` — [Order validation](/api/checkout/callbacks/validate.md)
- `POST /merchant_urls.upsell` — [Upsell recommendations](/api/checkout/callbacks/upsell.md)
- `POST /merchant_urls.upsell_validation` — [Upsell validation](/api/checkout/callbacks/upsell-validation.md)