Simply click on the relevant challenge and then fill in the standard order attributes as you are used to from any other online purchase. The form of payment is up to you, however there are a number of options, ranging from payment by payment cards from VISA/MS, FPX, GrabPay and many more (see full list: https://stripe.com/en-gb-cz/payments/payment-methods) or crypto. If you pay by crypto, we will refund all unpaired payments within 6-8 hours on business days. This is because  it allows us to minimize all the fees.