"The annual growth rate was generally low and below the rate of the recent months that would have shaped retailer expectations," he said in a statement.
"We also saw widespread discounting which appears to have accelerated the trend towards lower average transaction value," he said.
There continues to be growing use of scheme credit and debit cards which adds to the bank fees paid by merchants, he said.
And, to further pressure the bricks and mortar merchants, e-commerce growth has accelerated.
Most Paymark transactions are still with traditional bank — issued debit cards, totalling 70.7 million in December, but these were 2.1 per cent fewer than a year ago, Hopper said.
Across all cards, the average transaction value was $49.77, down 0.8 per cent on 12 months earlier.
"Anecdotally there were also many sales, starting back on Black Friday on November 23 , and this may have pushed the average transaction value lower as well," he said.
The busiest day of 2018 recorded by Paymark before Christmas was Thursday 20th December with $296 million worth of transactions processed.
The busiest period was at 12.16pm Saturday December 22 when a record 182 transactions per second were switched through the network.
Paymark said the first 23 days of the month showed that spending was up 1 per cent (excluding what Kiwis paid for fuel) on the same period in 2017.
- Staff reporter