If your customers are writing in letting you know discount codes aren't working, there are a couple of reasons we can generally point to that cause this.
The first thing to check is that the discount code is present in Shopify. Glow uses Shopify's native discount code feature so any codes issued by Glow should show in Shopify when you click "Discounts" in the Shopify navigation.
You may need to search for the code on this page to find it, but once you locate it, you'll see what rules apply to that code's usage. You can click on the table row for the code to see more rules associated with it and edit the configuration.
The top reason codes won't work for customers is that the rules for the code are more strict than the customer realizes.
Customer tries to place an order for less than the minimum order amount.
Customer tries to place an order without a specific product in it (if the code was for a specific product)
Customer tries to place an order without a product in a specific collection (if the code was limited to products in that collection)
Customer tries to place an order when not logged in (discount codes issued by Glow are only valid to the customer to which they were issued)
If the customers is using a free shipping discount and their shipping total was already zero.
If the customer has already entered a discount code or has an automatic discount applied by Shopify (Shopify only allows one code per checkout)
If you find you've made your discount code restrictions more strict that you wanted, you can update the Reward settings in Glow and update the existing codes which have been issued in Shopify.
Please let us know if you have any questions.
The Glow Team