To add credit simply go to the main menu and choose the Add Credit option. The packages are either 9.99, 19.99, 29.99, 49.99 EUR or US$ 12.99, 25.99, 38.99, 64.99. Select the payment package that would cover your estimated expenses and proceed to the payment screen.
It’s an in-app purchase on iPhone. On Android, use PayPal or pay directly with a credit/debit card.
Your balance will be updated immediately.