The discount will only apply to the first payment of the subscription order. Subsequent subscription orders will be at the full price. (Unless you manually apply it.)

This is because the first order is actually processed by Webflow and then Monto picks up subsequent charges, and we do not have a way through the Webflow API of seeing the discount code that the customer applied. (UPDATE: We are working on a possible way of applying the coupons going forward. We will edit this article if/when that happens.)

However! You can manually apply a discount code to a subscription inside of your Stripe account by creating the discount code that you want to apply (here) then finding and applying it to the relevant invoice (here).