Przelewy24 is an online payment system from Poland. The customer is directed to the website of Przelewy24 and can make the payment there, you will immediately receive a confirmation that the payment has been completed and can release the product immediately.
Note: This payment gateway requires an account at stripe.com with Przelewy24 payment enabled.
The configuration by WHMCS is very simple, only the API keys are needed for your Stripe.com account, and you can calculate the fees so that they are stored in the WHMCS transaction (fees are not passed on to the customer).