Some Amazon Prime Day shoppers are experiencing difficulty at the checkout. The issue appears when shoppers attempt to add an item to their shopping cart, on both mobile and desktop.
"We're working to resolve this issue quickly," Amazon tweeted.
It's still unclear if the outages are widespread, but they were reported in both the US and the UK.
This is Amazon's second Black-Friday-in-July flash sale. The much-hyped sales event is for members of Amazon's $99-a-year Prime subscription service. The ecommerce giant is expected to double its sales this year from Prime Day 2015, up to an estimated $1bn.
According to market research firm Slice Intelligence, last year's Prime Day was the second-largest sales day for Amazon in 2015, with total sales nearly 3.5-percent higher than Black Friday 2015. Only Cyber Monday surpassed Prime Day in terms of Amazon's sales last year.
A checkout glitch on Prime Day is certainly an embarrassment for Amazon, a company that prides itself on its technology stack. Last year's Prime Day also ginned up some negative buzz on social media, but mostly because key sale items quickly ran out of stock.