Why a customer can’t place an order from my shop

[lifeinacandleco]

A customer placed an order, but it got processed by Etsy saying it will take less than 72 hours to process the order. However, today the customer contacted me  saying her order was canceled and she can’t place another order from my shop anymore (no item found). I have never had this problem before, can anyone please tell me what’s going on. 

[UniqueGiftOrnaments]

Usually it's because the card is fraudulent or it has expired. Buyer need to check.

[Amaradorn]

Do you see the order or did it not come through to you? Is the item they want still available in your shop?

Is it possible that Etsy sent them an email telling them that it was sold out (in error - as seen on some other threads)