Australia Post’s SecurePay apologised to companies that have lost sales because of the transaction errors that have affected one of NAB’s bank payment gateways. The glitches have persisted for three days in a row.

Several companies using NAB Transact- a customised version of SecurePay- have criticised Australian Post for the three-day sales losses because of failed credit card transactions, timeouts, and bad gateway errors.

The affected agencies include IP Australia, a government patent and trademark agency. The agency took to Twitter to air out its apologies to complaining customers. “The @NAB Transact outage continues to affect our biz services and customers,” the agency said in a tweet.

On Wednesday, Australia Post released a statement saying that a service upgrade to SecurePay was successfully performed on June 2 to directly improve the platform’s capacity and security. Because of the unannounced upgrade of services to NAB Transact, the platform became unavailable. AusPost then apologised to customers who could not access the system.

“We remain committed to supporting NAB and its customers. All systems are currently stable and available,” the statement said.

NAB Transaction was put in “hypercare” by NAB on Tuesday to fix the error. At 6pm AEST Wednesday, there were still sporadic errors with credit card transactions. Also, businesses were receiving a “suspended status” when passing customer payments for batch processing and were asked to resubmit their file.

“Between 11pm [Tuesday] night and 8am [Wednesday], everything was back to normal, but then we started seeing error rates happening again”, said Marketplacer software developer Ryan Bigg.

Known international companies, the ones that use Paypal’s Braintree Payment Gateway such as Uber, AirBnB and many local companies such as Chemist Warehouse and SecurePay, were the most affected of the errors.

“We are working with our merchants affected by the NAB outages and immediately made fixes to minimise impact to their business,” a spokeswoman for Braintree said. “We will continuously evaluate the program as the situation evolves.”

A spokesman for NAB said on Wednesday evening that it was still trying to fix the problem and pinpoint the cause of it.

“We continue to work together with SecurePay, our secure payments provider, to resolve the issue with NAB Transact,” he said. “This is a high priority for us and our bankers are focused on supporting our customers through this.”