On one of its biggest sales days of the year, glitches have marred Amazon’s Prime Day.

Some customers are reporting difficulty making purchases because they can’t add items to their cart to check out. Amazon took to Twitter on Tuesday to address the issues angering customers looking for sweet online deals:

Some customers are reporting difficulty with checkout. We're working to resolve this issue quickly.

— Amazon (@amazon) July 12, 2016

Prime Day started in 10 different countries on Tuesday. It’s a 24-hour sales during which the company tries to get consumers to make summer buys on a range of discounted products including jewelry, clothing, electronics and pretty much anything else you can think of that the online retailer sells.

While only Amazon Prime members qualify for Prime Deals, the company is offering a free 30-day trial membership so buyers can take advantage of the savings.

Prime Day was started last year to celebrate the company’s 20th anniversary. Amazon proclaimed it shattered global sales records on the inaugural Prime Day with customers ordering 398 items per second.

After running into inventory issues last year, Amazon said they prepared a stock of TVs for Prime Day that is twice as big as Black Friday and Cyber Monday inventories combined.

Other online retailers like Walmart are offering deals to try to compete as shoppers stock on presents for a Christmas in July type purchasing bonanza.