Barclays suffered an IT glitch over the weekend that led to customer not being able to make payments in retail stores and through the bank's online banking portal.
Customers also suffered delays in receiving payments, including salaries, in their accounts.
The bank apologised for the inconvenience caused and moved to reassure them that the "technical issue" is now fixed and all services are working normally.“We would like to reassure customers that should they incur any fees or charges as a result of this incident, they will be refunded,” the bank said.
Barclays recently announced that it will focus more of its attention on the growth of mobile banking.
The firm's chief executive Antony Jenkins said that some Barclays branches may be closed to take advantage of the growing enthusiasm from consumers for mobile services.
All credits have now been applied to customers' accounts, but the downtime brought negative publicity for the bank on social media, as consumers took to Twitter to vent their frustrations.