Donald Trump paid a penalty fee of $2,500 to the IRS earlier this year after it had been revealed that his charitable organization had inadvertently violated tax laws with a $25,000 to a campaign group tied to Florida’s attorney general, the Washington Post first reported.

The improper transaction occurred in 2013, just as Florida Attorney General Pam Bondi was deciding whether she would investigate fraud allegations against the now defunct Trump University. Ultimately, she decided not to pursue the case any further.

“It was just an honest mistake,” senior vice president Jeffrey McConney said. “It wasn’t done intentionally to hide a political donation, it was just an error.”

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As a registered non-profit, the Donald J. Trump Foundation is not permitted to make political contributions, but the Washington Post, along with a liberal watchdog group, discovered otherwise in a batch of 2013 tax filings. Compounding the problem, the Trump Foundation failed to disclose the donation to the Florida-based group, apparently because it had identified the $25,000 donation as one that was going to support a Kansas charity with a name similar to that of the Attorney General’s political group, instead of the political entity supporting Bondi’s campaign.

The misconduct allegedly escaped notice until the Post notified them of the erroneous filings. McConney said, upon learning of the mistakes, Trump filed the necessary paperwork to disclose the donation to the IRS. He also paid the $2,500 penalty.