The way it should work (I've never used Paypal here, but have at other places), is after you select to pay via Paypal, you should be taken to a login prompt for your Paypal, and the rest of the purchase is conducted there. I've never had to input any card number if using Paypal (either the funds were in my account, or it was linked to my bank at the time for immediate transfer).

Now, depending how you set Paypal up, funds transfers can take a few days. Verify that the funds are actually available to use in your Paypal account.

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