If you're an Amazon Prime subscriber who's having issues making a purchase the retailer's big sale, you're not alone. The company tweeted this morning that some customers were having issues checking out. Replies to that post indicate that some customers are having trouble adding products to their cart as well. Amazon said it was "working to resolve this issue quickly," but the headaches are affecting eager customers during one of the site's biggest sales of the year. Today the company is holding its annual Prime Day sale, discounting thousands of items for folks who have a Prime subscription. We've reached out to Amazon for more information on the matter and we'll update this post when we hear back.