how can I pay for my apple id?

Apple ID are free, but to download apps you may need to enter a payment method.

Read the support article Add a payment method to your Apple ID - Apple Support about how to do that. The payment method may not be charged if you also have account balance or the item is free, but the payment method has to be present. This next article lists valid payment methods for different countries but note that in this situation Apple Account balance alone apparently may not meet the requirement and you need to use another payment method until you find one that satisfies Apple's requirement (often a credit or debit card): Payment methods that you can use with your Apple ID - Apple Support .