MIAMI— Southwest Airlines has fixed a technical issue that caused hundreds of flights to be delayed on Sunday, bringing service back to normal by Monday morning.

The glitch caused the delay of over 800 flights, equivalent to a quarter of 3,355 flights scheduled that day, causing problems on the website and mobile application of the carrier as well.

In order to check-in passengers, Southwest employees relied on back-up procedures, which caused lenghty lines at the airport counters. Passengers were asked to arrive at least two hours in advance to take their flights.

 

“It’s never too early to say thank you and to extend our apologies and we want to share those sentiments both with our hard-working Employees and our loyal and understanding Customers, whom we hope to welcome back for a better experience soon.  We’ll continue to work individually with our affected Customers to make this right,” Southwest said in a statement.