In addition to the revenue made on the day itself, it's a marketing opportunity for Amazon, which is always trying to sign up new Prime Members.
By about 4:30 p.m., many Prime Day links were working, and Amazon said later Monday that it was working to resolve the glitches.
Shoppers who went to the site looking to grab a sweet deal were greeted with images of cute dogs, and a message that read, "Sorry, something went wrong on our end".
It wasn't clear how widespread the outage was, and an Amazon spokesman didn't immediately respond to an email.
Amazon created Prime Day in 2015 to mark its 20th anniversary, and its success has inspired other e-commerce companies to invent shopping holidays.
The Amazon Prime Day sale lasts until tomorrow, and more deals will be coming over the next few hours.
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After the turmoil of the past 24 hours, it's hard to see how the Prime Minister can salvage the deal. Simon Clarke, a Conservative backbencher, said: "The (Chequers) deal is holed below the waterline".
"Prime members will enjoy a day (and a half) of our best deals, with 36 hours to shop more than one million deals worldwide", said Jeff Wilke, CEO of Amazon Worldwide Consumer. You can also go to this Amazon Canada page to access numerous Samsung deals. The majority of these offers are for its own products like Fire TV boxes or Alexa-enabled smart speakers, but the deals are hot. "They've got the Amazon Echos and the Dots and the little Amazon tablets in there".
Twitter lit up with screen shots of Amazon's Prime Day failures, which featured photos of dogs and the words "sorry". And even though retail has sprung back to life a bit this year-the SPDR S&P Retail ETF (XRT) is up 9.5% since the start of 218-it's still a big problem for the industry.
"They certainly feel like they have to compete because the first year they had a lot of counter sales". Chains like Macy's, Nordstrom, Best Buy, Walmart, and Target planned to roll out their own promotions, said Charlie O'Shea, lead retail analyst at Moody's.
Prime Day is expected to be one of the biggest sales days of the year for Amazon.
In Europe, Amazon employees were using Prime Day to draw attention to their complaints against the company.