Greggs said it expects to be able to take card and cash payments again soon after the bakery chain experienced issues with its tills.
In a statement, the bakery chain said it expects "the issue to be fully resolved shortly".
It added: "We apologise for the inconvenience this may have caused to our customers."
Earlier on Wednesday morning, Greggs said it was "working to resolve this as soon as possible" after issues prevented them from selling goods and resulted in shops being closed.
Users on X around the country reported that their local branches were shut or heavily affected, with some stores asking people to place mobile orders.
"Greggs in Westminster closed. Problem with tills," one person wrote, while another added: "Greggs this morning cash only! Sitting here with my coffee watching almost everyone have to walk out."
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Another person said: "Heart goes out to all those with hangovers this morning who were unable to buy anything at Greggs."
It comes after "technical issues" affected Sainsbury's in store contactless payments and online delivery services at the weekend, causing chaos for shoppers.
Tesco cancelled some online orders too after suffering issues.
Last week, McDonald's customers were turned away from restaurants around the world, including in the UK, after the fast food chain was also hit by major IT problems.
cyber attack claims a 'real worry' for companies
There is no evidence to suggest that the tech outages at four of the UK鈥檚 best known retailers were linked.
McDonald鈥檚 said a 鈥渃onfiguration change鈥� was to blame for the global outage that forced outlets to close on Friday. Meanwhile, Sainsbury鈥檚 blamed the glitch that hit online deliveries over the weekend on a 鈥渟oftware update鈥� while Tesco experienced an unrelated issue that also affected deliveries.
Greggs has been tight-lipped about the fault that put tills across the country out of use on Wednesday morning, but has since said that the issue has been resolved.
None of these companies said they suffered a cyber attack that led to these technical failures, but McDonald鈥檚 was quick to stress that malicious actors had nothing to do with it.
Their haste reflects the fact that being associated with a cyber attack is a real worry for companies as consumers become increasingly literate about access to their data and concerned that it could fall into the wrong hands.
But the reality is that cybersecurity issues are one of the biggest threats on the horizon for businesses. The majority of larger UK businesses have fallen victim to a cyber security incident in the last 12 months, according to new figures published by the government on Wednesday.
The other side of this unfortunate series of events is that a spate of unrelated major technical glitches among some of the UK鈥檚 biggest retailers prompts the question: is it purely coincidence or are these sorts of outages becoming more common?
Greggs operates more than 2,450 shops across the UK. It's unclear how many stores were affected.