A Kiwi living in Australia isn't sure what to do with the cost of living payment she "received in error" on Monday.

The first $116 instalment of the payment was automatically sent out today, with more than two million Kiwis entitled to the money.

To be eligible, a person must be a New Zealand tax resident aged 18 and over who earns below $70,000 a year and who is not receiving the winter energy payment. The initiative is projected to cost $816 million, announced in Budget 2022.

But Charlotte Castle, who has been living in Australia for six years and who earns more than $70,000, got her first payment on Monday.

When she was first emailed by the IRD, Castle "thought it was a spam email".

"So I was quite surprised to actually go to the IRD website and read the official mail and find the payment had actually gone into my bank account already when I checked this morning."

She says she isn't sure what to do with the money and might transfer it to family in New Zealand.

"Cost of living has gone up here, so I could certainly use it towards meeting my expenses here, in Australia, however I do feel a degree of guilt in doing that because, I didn't need the payment and I certainly feel that... I've received it in error, really."

National's Finance spokesperson Nicola Willis told 1News that she has heard about many more cases like this one.

"I suspect this is just the tip of the iceberg. As people go to their email accounts and open them over the next few days, they too will realise they've got a note from IRD... the scale could be enormous.

"I think the minister owes it to hard-working New Zealanders to investigate this further."

Associate Minister of Finance David Parker said the payments were targeted.

"There was always going to be a small number of people who were paid out according to the most up-to-date data that Inland Revenue held that are not eligible for it, sometimes through no fault of their own.

"The alternative would have been to require 2.1 million people to make an application which would have both cost more money than the money saved and would have delayed things so that the payment could not have been made quickly.

"If people think they've received it by mistake, they can pay it back. We're not going to chase people."

The next two $116 instalments will come on September 1 and October 3.