SYDNEY, Australia — A court in Australia upheld an order on Friday for Elon Musk’s X to pay a fine of 610,500 Australian dollars ($418,000) for failing to cooperate with a regulator’s request for information about anti-child-abuse practices.

X had challenged the fine, but the Federal Court of Australia ruled that it was obliged to respond to a notice from the eSafety Commissioner, an internet safety regulator, seeking information about steps to address child sexual exploitation material…