# Checkout links

> A URL that opens a product's checkout already filled in: coupon, quantity, option and affiliate. No record is stored, so it never expires.

Page: https://sellstamp.com/docs/developers/checkout-links

## The link

Build one under **Marketing → Buy links**, or write it by hand:

```
https://your-store.example/buy/my-plugin?coupon=BLACKFRIDAY&qty=3&variant=<option id>&aff=<affiliate code>
```

`/buy/<slug>` is the product’s own checkout under a shorter path. It is kept out of search results and points search engines back at the product page.

## Parameters

- **coupon**: Fills in the discount code. The coupon's own rules still decide what it is worth.
- **qty**: Sets the quantity, for a product with quantity deals.
- **variant**: Pre-selects one of the product's options.
- **aff**: Credits an affiliate, exactly as their own referral link would.

## A bad parameter is dropped, never an error

A link pasted into a newsletter lives for years, so it must not break. Every parameter is checked against what the product offers right now, and anything that no longer fits is dropped:

- An expired, used-up or too-small-order coupon arrives as an empty box.
- A quantity above the limit is lowered to the limit.
- An option or affiliate that no longer exists is skipped, and the rest of the link still works.

The customer can change anything the link filled in.

## What a buy link is not

A saved record. There is no list of links, no click counter and nothing to revoke. Whatever a link carries that belongs on the order, the coupon or the affiliate, shows up on the order.