An Irish customer of finance app, Revolut, was incorrectly told that the balance of his account was almost €200 million.
Kevin Conway's Revolut app displayed the multi-million euro error for almost two hours before the issue was corrected.
The Wexford man said his account balance should have been around €200 as he uses it for travel and small transactions.
"It was around 3pm or 4pm on Friday of last week and I checked my app and it said I had a balance of €197m," Mr Conway said.
On discovering the mistake he checked the app repeatedly but it continued to display the incorrect amount.
"Then all of a sudden it was gone," he explained.
"I didn't know what to do. I was scratching my head. I was €200m richer for two hours there."
"I had lots of things racing through my head - what do you do with €197 million? Should I go to the Cayman islands, should I pay off my car?" Mr Conway said.
"I knew in my heart and soul I couldn't do anything with the money, so I was waiting to see what would happen."
Revolut said that the issue was a "temporary bug".
The company said the error was an incorrect display in Mr Conway's app and the money would not have been available had he attempted to access it.
"This had no impact on the funds in that account and the error was quickly corrected by a customer support agent."
Mr Conway contacted Revolut customer support who joked that they wished the funds had been real.
"I wish we could do it. I would make myself rich and you as well!" an agent joked in a webchat.
There is a precedent in Ireland that customers are not permitted to benefit from a bank error and a number of people have been prosecuted for theft in recent years having spent money incorrectly lodged in their account.
Revolut has grown to around 450,000 users in Ireland since it arrived in the country three years ago.
It is covered by a European E-Money licence and has a banking license in Lithuania.