Google Play processes all purchases made via the in-game shop.  You can purchase digital content on Google Play using payment methods from your Google account. If it's your first time making a purchase, your payment method will be added to your Google account. 

Available payment methods vary by country; listed below are the best available methods:

• Credit & debit cards: Visa, MasterCard, Amex, additional country-specific cards (e.g. Elo credit cards in Brazil)
  
• Carrier Billing: depending on customer country and carrier (full list available here)
  
• Google Play gift cards: available in selected countries (full list available