You will need to pay for YAZIO PRO directly through your iTunes account, typically by credit card or with your account credit.
Note: If you go PRO, the payment will be charged through your iTunes account during purchase confirmation. The subscription will be auto-renewed shortly before the subscription period ends, maintaining the same price and subscription type you previously purchased, unless you unsubscribe no later than 24 hours before the subscription ends. Subscriptions can be managed through your iTunes account after purchase. It is not possible to refund a subscription or cancel a subscription during the current period.