Train passengers had problems buying tickets all afternoon (Tuesday 30 October) after a payment system malfunctioned.
Govia Thameslink Railway (GTR) was one of the companies affected by the problem and blamed the MasterCard “payment portal”.
The glitch affect card-only payment machines and was described as a “network-wide issue”.
GTR, which runs Southern, Thameslink and Gatwick Express services, said: “The problem with cards not being accepted at ticket machines on our network and elsewhere in the country began earlier this afternoon and was resolved at around 5.40pm.
“During this time, staff at Brighton redirected passengers either to the travel centre to buy their tickets or to on-board supervisors who would have been able to sell tickets from their hand-held ticket machines.
“The source of the problem with our ticket machines has been confirmed to be the MasterCard payment portal. This is affecting businesses around the country.
“The problem is now fixed. The source of the problem is also not entirely clear.”
The glitch affected other train operating companies and tram services around the country.
Mastercard said that it was not experiencing any issues with its network.