Customers across the UK and Europe have been unable to pay for their purchases with Visa cards because of a network failure.
Shoppers reported they were stuck in queues in supermarkets and petrol stations as Visa transactions could not be processed.
Some banks have advised customers that they can still withdraw cash from ATMs.
Visa says it is working to resolve the issue. Mastercard and American Express said they were not affected.
Paymentsense, which runs card services for small businesses, said some transactions were now starting to go through but there was a backlog.
Responding to complaints on social media, HSBC said there were issues with processing Visa payments, which were intermittent, but were “slowly recovering”.
Jay Curtis, from Swansea, had two cards declined in B&Q when tried to pay for £240 worth of goods.
“My card just wouldn’t go through,” the 32-year-old told the BBC.
“I didn’t have cash on me so I had to drive all the way home.”
Elle Gibbs-Murray, from Bridgend, said she was stuck in traffic on the Severn Bridge for 45 minutes as drivers were unable to pay the toll by card.
Adam, from Manchester, is a on a canal boat holiday with his girlfriend, Rach, and he is unable to use his card.
The 26-year-old said: “We have spent all day boating to moor up at a riverside pub in Kidlington for a birthday meal only to find the visa payments are not working. Having only £20 between us we have had to opt for a birthday drink instead.
“[There is] no cash point for miles around and no car as we are on the canal boat.”
Supermarket Tesco said chip and pin payments were not affected, but contactless payments were.
Sainsbury’s also said it was experiencing problems.
Banks, including the Bank of Ireland, have said cash withdrawals at ATMs can still be made.
We are aware some customers are experiencing Visa debit card issues. This is impacting multiple banks across Europe. We will update when we know more. Cash withdrawals can be made at any BOI ATM.
— Bank of Ireland (@talktoBOI) June 1, 2018
End of Twitter post by @talktoBOI
The Bank of England, which oversees electronic payment providers such as Visa, said it was “aware of the issue” and was “working with the firm to resolve the situation”.
Transport for London said it expected customers to still be able to use their contactless payment cards to pay for travel on its buses, trains and Tubes.
However, Paymentsense, which runs card services for small businesses, said transactions were now starting to go through but there was a backlog.
Are you a Visa customer? Have your card payments been affected? You can share your experience by emailing email@example.com.
Please include a contact number if you are willing to speak to a BBC journalist. You can also contact us in the following ways: