Amazon faced serious website issues on one of the site’s most important days of the year — Prime Day, when many items are heavily discounted.

CNBC reports that e-commerce giant Amazon faced a number of glitches and issues following the launch of Prime Day, one of the companies biggest sales of the year in which items across the website are heavily discounted. Prime day began at 3 p.m. on Monday and takes place for 36 hours, marking the longest Prime day in Amazon’s history.

However, Amazon shoppers quickly reported many site glitches when attempting to access Amazon. The company acknowledged these issues in a tweet which noted while there were some problems, many customers were managing to operate on the site with no problems: “Some customers are having difficulty shopping, and we’re working to resolve the issue quickly. Many are shopping successfully — in the first hour of Prime Day in the U.S., customers have ordered more items compared to the first hour last year.”

Many users were redirected to an error page displaying “dogs of Amazon” when they attempted to enter the site following the start of Prime day. Others got stuck in a redirect loop with pages repeatedly telling them to “Shop all deals,” clicking any category returned users to the “Shop all deals” page.

Some users managed to shop successfully only to receive a page telling them that the site was experience “unusually heavy traffic” when trying to check out.

GlobalData Retail Managing Director Neil Saunders commented on the glitches saying: “The outage is especially problematic as many of Amazon’s Prime deals are promoted for a set window of time — something that could cause a great deal of frustration for potential customers.”

Analysts have estimated that Amazon could make approximately $3.4 billion in the 36-hour Prime Day window, but Amazon stock was falling by approximately 1 percent in after-hours trading following news of glitches.