MIAMI — When elections officials in Palm Beach County emailed ballots last week to military and overseas voters, they failed to notice a typographical error: The name of Gov. Tim Walz of Minnesota, the Democratic nominee for vice president, was misspelled as “Tom Walz.” The office was made aware of the error less than 18 hours after the ballots went out, Wendy Sartory Link, the county’s elections supervisor, said Sunday. “The error was isolated to 257 electronic ballots,” she said in an email, adding that the misspelling had been “immediately corrected.” The affected voters were emailed a recommendation to download the updated ballot, she said. The New York Times learned of the error from a concerned voter overseas who sent the newspaper a screenshot of her misspelled ballot.