Your payment is processed when you place your order. For more information or details regarding your transaction (fees, installments, etc), please reach out to your payment processor.
Here is how you can contact Affirm: https://www.affirm.com/help/
Here is how you can reach Klarna: https://www.klarna.com/international/customer-service/
Here is the contact for Paypal: https://www.paypal.com/us/smarthelp/contact-us