Don't sign in with Paypal. click on the gold Paypal button, and then at the bottom of that page you'll see it says "pay with credit or debit card". You don't have to have a paypal account. There is a message on the site that says that, but it's not as visible as it should be.
Paypal is a payment service that allows credit card payments in addition to PayPal account payments. Anyway, hats off to Sam's for doing such a great job of creating contactless experience.
Wish I could help you out and tell you why. That is strange they wont except your card. If you're not far its total worth the drive.
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