An invalid tracking number may be due to an input error by the seller or the logistics provider not processing the order correctly. Contact the seller to verify if the tracking number is correct and ask them to provide the correct information again. If the tracking number is correct but still can't be queried, it may be a system issue with the logistics provider, and you can contact their customer service for inquiry. If the seller cannot provide valid tracking information, you can request a refund or reshipment from the seller.