Square was hit by an hour-long outage yesterday evening, stopping some payments being processed.
The outage caused problems for users of the startup's website, Squareup.com, as well as its mobile app, The Next Web reports.
Square spokesman Aaron Zamost told the publication:
"Some users experienced a connectivity issue late this evening, during which time our website was inaccessible and some payments could not be processed. The issue was quickly recognized by our engineering team and has been fixed. We're sorry for any inconvenience this may have caused and we're taking the appropriate steps to ensure it doesn't happen again."
Square allows merchants to take credit card payments using its free Square card reader, which plugs into iOS or Android mobile devices. The company processes $5 billion of transactions per year.
The startup this month. Some 7,000 Starbucks outlets will introduce Square's mobile payment system this fall, and the coffee chain also invested $25 million in the mobile payments startup.
Square recently introducedfor merchants who use its platform, removing the 2.75 percent per-swipe fee for customers in favor of a $275-a-month payment.