Create a checkout object

## Checkout properties
AttributesData typeDescription
**merchant**
<span style="color:red">required</span>_object_Merchant specific information. See [details](🔗﻿).
**shipping**
<span style="color:red">required</span>_object_The [shipping details](🔗﻿)﻿
**billing**_object_The [billing details](🔗﻿)﻿
**items**
<span style="color:red">required</span>_Array_An array of [item](🔗﻿).
**discounts**_object_A list of [discount](🔗﻿). Each discount must have their discount code.
**metadata**_object_See [details](🔗﻿).
**order_id**_string_The merchant order id. This is stored for your own future reference.
**financing_program**_string_A financing program applied on this checkout.
**shipping_amount**_integer_The total shipping amount in cents.
**tax_amount**_integer_The total tax amount in cents.
**total**
<span style="color:red">required</span>_integer_The total amount of the checkout in cents.
**checkout_expiration**_timestamp_A date-timestamp of when the `checkout_id` will expire.

- ISO timestamp format
- No milliseconds