Append your code to your store url:
The url above shows you how you could link to your store with a discount code. Once enabled, the code will automatically be applied during checkout. The important part is to append ?discount=[YourDiscountCode] after your shop url.
Unfortunately the app doesn't work for all stores in the current situation where some have custom-built carts that we don't support. If it doesn't work for you, please contact us and we will try to add support for your store, chased together, you help us to become even better.