Use resellers. You can find the list of them on the official Tibia webshop.
Be wary of suspiciously low prices though, as these could be scams. Always double-check the seller’s reputation and avoid trading with unknown or untrusted players as some players might create fake offers to manipulate the market prices. Be cautious and always verify the legitimacy of the offers before placing your order.
Note: some certain payment methods you use can delay coin transferability by 6 months. So if you need your coins transferred immediately, select the Tibia Coins (transferrable) tab during checkout and pick a supported payment option that does not force a security hold in your region. Take note of this.
And more importantly, use a card you have complete ACCESS to cos they expect the payment method's name to match the account holder's registered details, although they still allow family or friends payments. However, mismatched names can trigger AFA which is Automated Fraud Alerts, (you don't want this to happen) cos if the owner of the card you're using disputes the charge or requests a chargeback through their bank, your Tibia account will be permanently banned, deleted or frozen almost instantly for fraudulent payment.