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Amazon Hit with Checkout Problems on Prime Day

July 12, 2016, 3:07 PM UTC’s (AMZN) Prime Day on Tuesday was marred with many customers reporting problems checking out, potentially denting business on a day the online retailer is hoping will yield hundreds of millions of dollars in sales and spur sign ups to its Prime program.

On Tuesday morning at 7:40 Eastern time, the retailer said on Twitter that some customers were having problems with the website. At 11:18 a.m., or two and half hours later, the company told Fortune by email that the problem had been resolved.

But by then, Amazon was dealing with angry shoppers. Earlier, some customers took to Twitter to also complain about problems like adding items to carts. And by early morning, the hashtag #PrimeDayFail, which gained traction during last year’s inaugural event after many customers were underwhelmed by items included in the deals, was trending again.

The snafus were poorly timed for the online retailer, whose $81 billion in annual sales make it the largest e-commerce player in the U.S. by far, doing six times more business than (WMT). Still, investors shrugged off the problems as the stock hit an all-time high on Tuesday.

Amazon debuted Prime Day last year as a one-day sale exclusively for members of its Prime subscription shopping service. The company’s goal is to create a new shopping holiday like Black Friday—the busy shopping day after Thanksgiving—to encourage more spending on its site. While Prime Day is a manufactured shopping event, the sale is a big deal for Amazon: retail advisory firm FBIC, has forecast predicts Prime Day could generate $525 million in sales, up 26 percent from its $415 million estimate last year.

The larger point for Amazon is to stoke enrollment in its Prime service, which for $99 a year, among many benefits, offers customers free two-day delivery and access to Amazon’s TV and movie streaming service. Prime enrollments peaked on July 14 last year, one day before Prime Day. According to comScore data, 21.7 million unique visitors went to on Prime Day last year, making it as big a deal as Cyber Monday. And Consumer Intelligence Research Partners estimated this week that 63 million people in the U.S. are Prime members, up 43% from a year earlier.

Amazon’s Prime Day has prompted many traditional retailers to hold their own events. Most notably, Walmart this week waived minimum online order sizes to get free shipping.

The Amazon snafus are reminiscent of website problems retailers like Target (TGT), Best Buy (BBY) and Neiman Marcus have all dealt with in the last few years on major online shopping occasions.