WhatsApp started to return to operation at around 2:10 a.m. Pacific Time, providing relief to billions of users and businesses that rely on the Meta-owned instant messaging and calling app.

WhatsApp said a technical error caused the issue. “We know people had trouble sending messages on WhatsApp today. We’ve fixed the issue and apologize for any inconvenience,” a Meta spokesperson said.

Earlier in the day, users across the globe started to complain that they were unable to send or receive new messages, sign up for WhatsApp, update their profile information or access privacy settings, they said.

DownDetector, a web service that tracks services performance, said tens of thousands of people complained about the outage when WhatsApp was down. WaBetaInfo, another popular service that tracks WhatsApp, reported that the issue was “server-side,” meaning users couldn’t do anything to resolve the issue.

In an earlier statement to TechCrunch, a Meta spokesperson said the company was working to restore WhatsApp for “everyone as quickly as possible.”

WhatsApp has become critical infrastructure in many markets, used by government officials, telecom service providers and, of course, billions of people. As of 2020, the service was being used to send over 100 billion messages a day, a figure that is unrivalled in the industry.

Facebook Messenger and WhatsApp together were used to exchange 60 billion messages a day as of early 2016. Apple chief executive Tim Cook said in May 2020 that iMessage and FaceTime were seeing record usage, but did not share specific figures. The last time Apple did share the figure, it was far behind WhatsApp’s then usage (podcast). WeChat, which has also amassed over 1 billion users, is behind in daily volume of messages, too.