Auckland Transport has conceded it could improve its online payment website after $342,000 of top-ups for the AT HOP travel card lapsed unloaded in the past year.
The agency said the problem was customers not using the cards within 60 days of a top-up, a requirement spelt out in its terms and conditions.
Overall, 14,500 cardholders failed to have the balance loaded in the past year, and many have said they were unaware of the rule.
Nowhere during the top-up process on the agency's website is there a message alerting cardholders to the 60-day rule. The final step in the payment process is a bold message, which reads "Your Top Up is Successful".
"Could we have a message on there that says 'now go and tag on in the next 60 days' - that's probably the case, yes," Auckland Transport CFO Richard Morris said.
Mayor Phil Goff agreed that was a move that could be easily made.
"It seems to me they could improve on that and give advance warning, rather than just email when you are coming close to the expiry date," Mr Goff told RNZ.
Mr Morris said overseas cities with similar ticketing technology had similar expiry rules, although some were longer than 60 days.
The agency said only a limited number of uncompleted top-ups could be held in the system before it began to slow the processing of passengers tagging on and off journeys.
Customers whose top-ups lapsed could have the balance reinstated by contacting the agency.
Mr Morris said he was confident that those at risk of having their top-ups lapse were receiving warning emails.
The 60-day rule has existed since the AT HOP system went live in 2012, and AT had acknowledged cardholders' money was being held in the system.