I think that this is the case, from the reporting it seems like it’s just their payment infrastructure that is affected. Likely they could handle cash transactions just fine. It’s just that the vast, vast majority of Swedish customers don’t use cash anymore, so it’s not worth it to keep the stores open until it’s fixed.
Going cashless is extremely common for customers in Sweden. They would get so few customers (everyone would just go to the next grocery store), and the aggravation it would cause from customers who haven't heard the news and can't pay probably just makes it not worth it to have them open. Take the loss, fix the issue, reopen all the stores when it's done.
