Mr. Trump had argued that an inquiry by the attorney general, Letitia James, violated his constitutional rights. It was his second legal loss in two days.
The judges unanimously rejected the former president’s appeal of an earlier ruling that ordered him and two of his adult children to testify in a civil investigation into his family business.
In a settlement, the software company admitted no wrongdoing but agreed to repay fees it had charged millions of Americans for returns that the authorities said were falsely advertised as free.
Former President Donald J. Trump was ordered to turn over materials sought by Letitia James, the New York attorney general, and will be fined $10,000 per day until he does so.