Action Details
Requirements and how-to articles for Etsy's action:

paid action
A coupon is a code that may be redeemed for a discount on an item or free delivery. Coupons are not displayed publicly; as a seller, you may create and distribute coupons at your discretion.

You need this to get it done:

Coupon Type
Choose the type of discount your coupon is offering: percentage off (you can offer any percentage off the list price of items in your shop), fixed amount off (you can offer a fixed amount off the list price of items in your shop) or free standard delivery.
Coupon Code
Create the coupon code to be sent to shoppers which they can enter into their basket at the checkout.
Must contain between 5 and 20 alphanumeric characters (no spaces or punctuation.)
Minimum Purchase Amount (optional)
If you wish, you can enter a minimum purchase amount which the customer must spend in order for the coupon to apply to their basket.
Requirements missing or found errors? Report

How-To Articles
A list of useful links for you:

Etsy - Advertising & Marketing Policy
Etsy's official policy for advertising and marketing, which is part of their terms of use.
Etsy Help Centre - How to Set Up Sales and Coupons for Your Shop
Official information about setting up sales and coupons on Etsy.
Etsy - Organising a Productive Promotion for Your Shop
Official help guide for Etsy shop promotions.
Link missing here or found errors? Improve How-Tos