If you would like to enable customers to apply their own discount codes to an upcoming recurring order from the "Manage Subscription" page, follow these steps:
- From "Shopify Admin", select Apps.
- Select Recurring Orders & Subscriptions by Bold.
- Select Settings.
- Select General.
- Scroll down to "Customers Can Change Their Discount Codes", select Enable.
- Select Save.
Note: Visit Apply a Discount Code to an Existing Subscription to do this for your customer.