Depending on your fee schedule, you may incur fees to refund a charge. Additionally, Stripe's processing fees from the original transaction will not be returned in case of a refund.
A large portion of the underlying cost of payment processing is driven by fees assessed by banks and payment networks (like Visa and Mastercard). These networks set rules about which fees apply for refunded payments, and in many cases banks and card networks keep the entire upfront cost of a refunded transaction. For some regions and payment types, refunded payments also incur additional fees.
We aim to make our pricing simple and transparent, and our standard fees include access to a variety of features like fraud protection, reporting, and other tools for managing your payments. To address these underlying payment processing costs and continue providing these services as part of our standard pricing, Stripe does not return our fees when a payment is refunded.
Refunds (Stripe Docs)