United States President Donald Trump officially revealed his reimbursement to his lawyer, who paid Stormy Daniels to shut her claims of an affair.
On Wednesday, the Office of Government Ethics found that Trump ought to have unveiled the payment in his previous financial disclosure.
The filing shows he paid Michael Cohen between $100,001 (£75,000) and $250,000 for expenses incurred in 2016.
Trump previously denied knowing of the $130,000 payment to Stormy Daniels.
The White House stated in a footnote to the filing that it was listing the payment "in the interest of transparency", and contended it did not have to make the disclosure.
However, the head of the Office of Government Ethics (OGE) wrote in a letter that "the payment made by Mr Cohen is required to be reported" in the liabilities section of the statement.
In his letter to Deputy Attorney General Rod Rosenstein, the OGE acting director said: "You may find the disclosure relevant to any inquiry you may be pursuing."