Popular Bitcoin exchange Coinbase has been overcharging users thousands of dollars, blaming a bug linked to how credit card companies bill for the service.
Coinbase said it has fixed the problem which saw customers charged multiple times for transactions, while it has promised refunds to those affected.
Coinbase put the error down to changes in MMC code, the code used by Visa to identify credit and debit card transactions. The Visa changes came as multiple banks said they would no longer allow users to buy cryptocurrencies using credit cards.
“Coinbase will ensure that each affected customer will be refunded in full for any erroneous charge,” the company said. “We deeply apologize for any frustration this may cause. We are actively working with banks, processors and networks to improve the digital currency purchasing experience.”
On Coinbase’s Reddit forum, one user complained of a $67,000 charge, another of a $17,000 hit. A Coinbase spokesperson responded to both comments offering a refund and advising users to contact its support line.
Coinbase is one of the most popular online cryptocurrency exchanges, with around 10m users. It was the top app in Apple’s App Store over the Christmas period as interest in cryptocurrency boomed.
The San Francisco company has emerged as one of the most successful cryptocurrency startups, but has been hit with problems due to the massive demand for Bitcoin on its platform. The sudden rise and fall of Bitcoin, which briefly recovered to $10,000 this week, has previously caused Coinbase to shut down its platform during particularly volatile period of trading.
In December, Coinbase CEO Brian Armstrong warned users the service could become unavailable “during times of significant volatility or volume”.