The train operator posted on social media that a number of people had been in contact to complain about the issue.
It warned the problem was affecting various stations, but did not mention which ones.
It said: “I’ve received a lot of messages this morning to say our ticket machines are displaying an error message at various stations. Sorry for any inconvenience this may cause.

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“We’re working to fix this asap. Tickets can still be purchased from ticket office, app and onboard train.”