Sezzle Inc., the Minneapolis fintech firm that went public in Australia this summer, said Monday that from July through September it experienced the biggest jumps in new retailers and customers yet for its buy-now, pay-later platform.

It also reported huge gains in the volume of transactions and the fees they generated for the company. Its net cash flow remained negative, widening to $7 million, though the firm has a cash pile of more than $27 million.

The results helped push Sezzle shares to a near-record close of A$2.71 on the Australian Stock Exchange, the highest level since their second day of trading in late July.

"We are very pleased to report ongoing strong results," Charlie Youakim, the company's co-founder and chief executive, said in a statement.

The number of merchants using its platform for completing online sales grew 49% to 7,507 from 5,048 at the end of June. Sales by those merchants amounted to $68.8 million, up 64% from the June quarter and the fastest pace in the company's history.

Those sales produced $3.6 million in fees for Sezzle, the main source of the firm's revenue. That's up 69% from the $2.1 million in fees it collected in the previous quarter.

Sezzle said net transaction losses continue to improve, though it didn't provide specific figures.

Sezzle developed and provides an alternative to credit card payments for online shoppers. Retailers offer the Sezzle system as an option at checkout alongside credit cards and PayPal. By using the option, consumers complete a purchase and then repay Sezzle for the amount in several installments over six weeks.

Such payment systems are more widely used in other countries, such as Australia. Sezzle and Australia's Afterpay Touch Group Ltd. and Splitit Ltd. are racing in that country and elsewhere to deploy the systems.