The Government has admitted it "inadvertently" paid Tukoroirangi Morgan twice for Treaty-related work a week after being asked for assurances in Parliament that this wasn't the case.
In two incidents, Mr Morgan was overpaid $26,325 of his $171,093 fee.
In 2009, Mr Morgan negotiated the Waikato River settlement on behalf of Waikato-Tainui. However, at the same time he was working for the Government as a Crown facilitator to move other iwi through the settlement process.
Last week, Act MP David Garrett asked Treaty Negotiations Minister Christopher Finlayson if he could guarantee Mr Morgan wasn't charging twice for work completed for the Office of Treaty Settlements and Tainui.
Mr Finlayson replied the Crown paid only for work completed for it - what Tainui paid Mr Morgan was its business.
However, on Wednesday, the minister asked the House if he could correct his answer as it had since come to his attention that there were two instances last year when "Mr Morgan was inadvertently paid twice for the same work as a Crown facilitator".
Mr Morgan repaid the full amount for the first invoice within 24 hours, and the Office of Treaty Settlements expected repayment of the second invoice within the next week.
"He was unaware of the double payment and has undertaken to repay that amount," Mr Finlayson said.
"Accordingly, while it is correct Mr Morgan has been paid $171,093.61, he should have been paid $144,768.61."
A briefing paper from the Office of Treaty Settlements said it took responsibility for the double payments for the invoices where one was worth $18,225 and the second $8100.
The administrative error in the second case occurred because of a duplicate email. The first case occurred because the invoice had been emailed and then posted.
Mr Morgan did not return calls and Mr Finlayson did not respond to Herald questions.
Mr Garrett was still concerned there was an "absolute" lack of transparency around what Treaty consultants were paid.
He said it wasn't good enough that it took the minister two attempts to provide accurate information. "This is taxpayer money. Every dollar of it is taxpayer money. It seems the only people getting rich [from the settlements process] are consultants and the like."