DALLAS (CBSDFW.COM/AP) – For the second straight day, customers of Southwest Airlines are running into problems when trying to manage reservations on the airline’s website.

Southwest Airlines posted an apology Tuesday to customers who were having difficulty on the website or the carrier’s mobile app. Some customers said on Twitter that they were unable to check in online for flights.

Southwest Airlines representatives did not immediately comment but, on Monday, a spokeswoman blamed the difficulties in making or changing reservations on a problem with the airline’s new reservation system, which uses information technology from Madrid-based Amadeus IT Group.

Amadeus representatives did not immediately respond to a request for comment. Earlier this year, Southwest Airlines became the first of the four biggest U.S. airlines to use the Amadeus reservations-system platform called Altea.

Despite saying Monday that the issue had been resolved, many Twitter users continued to report otherwise on Tuesday.

(© Copyright 2017 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)