How can I add paypal to iTunes?

To change your payment method log into the account e.g. Account > View My Account menu option on your computer's iTunes and add select PayPal : Payment methods that you can use with your Apple ID - Apple Support

If you change your payment method to PayPal, you might be asked to verify your account. If you are, you'll receive a verification code either through a text message to the phone number on file with PayPal or instructions to get the code through a code generator. If you can’t access this verification code, you might need to sign in to PayPal to update your phone number or contact PayPal for more help.

PayPal is only available in Australia, Austria, Belgium, Canada, Finland, France, Germany, Greece, Ireland, Israel, Italy, Luxembourg, Mexico, Netherlands, Portugal, Spain, the United Kingdom, and the United States.

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