Click on the pay button, then log into your Paypal account. When you are at the "complete payment" screen, you will then go down to where you see your payment options. You will see the highlighted option that says "more funding options," click on that. There you will be able to see all your credit/debit cards, and click on what you want to pay with. You can also change the backup funding source there as well.

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Your friend is your needs answered.
Kahlil Gibran