This article covers
Will plan price merge var display the price of the plan after the discount?
With respect to the merge_vars added in the email notification, these would be the details of the customer's subscription plan price.
For example, if the product catalog plan price is 500$, and a customer had subscribed to the plan for the amount 300$, then the plan price would be displayed as 300$.
If in case, the subscription plan price is 500$, a coupon is 50% then still the plan price is 500$ but the invoice amount would be 250$.
So, the merge var - Plan Price will be 500$. In order to display the invoice amount after applying the coupon, use the Estimated invoice amount token. Screenshot for reference:
Alternatively, you can also include a subscription summary in the email notification.