Discounts are not applied to subscription upgrades
We always try to implement best practices that meet our customers needs, especially regarding discounts to make the most of it. However, we should let you know that with the way our service works, discount coupons are only applicable to new subscriptions, they don't work with upgrades. When you upgrade your subscription from one plan to another, there is no option to apply a discount.
Here you can find detailed information about available discounts - https://help.elfsight.com/article/393-available-discounts.