Train passengers were unable to buy tickets online with several operators of a major retailer due to a technical glitch.
Among the operators who reported being affected by the issue on Tuesday morning were Greater Anglia, Northern and Southeastern.
Trainline, the UK's largest train ticket retailer, was also hit by the fault.
Greater Anglia and Northern said the fault meant passengers could not make card payments on their apps or websites, while Southeastern warned that ticket-buying at stations was also affected.
A spokesman for Greater Anglia (GA) said: "There is an ongoing problem with the GA app and website regarding making card payments.
"This is currently being investigated and will be fixed as soon as possible."
Northern said in a statement: "We are aware of an issue with our app/website whereby customers cannot complete their booking. This is being looked into and we hope to see a fix soon.
"In the meantime please use ticket-buying facilities at stations to purchase your tickets."
Southeastern posted on Twitter: "We are aware of an ongoing problem with making card payments at present, at stations and via online channels for ticketing.
"Teams are investigating currently and looking to fix as soon as possible. More details shortly."
Trainline told customers that its booking system was "experiencing a technical glitch", before later stating that "all booking services are back up and running".
The Rail, Maritime and Transport union, which has claimed there are plans for a mass closure of station ticket offices, tweeted: "Numerous train operating company ticket purchasing apps, and Trainline, are down this morning.
"This merely highlights the short-sightedness of Government plans to close up to 1,000 ticket offices."