The DHL Shipment Tracking - Unified API will provide a general response when a supported tracking ID is requested. However, sensitive data like like the different cities where a shipment has passed by, won't be disclosed unless the user fills in the correct "recipientPostalCode" parameter value, this is called "the postal code challenge".
The Postal Code Challenge is a feature within the Unified Tracking API that allows users to retrieve shipment data with enhanced privacy and security measures. This feature aims to ensure the privacy and security of sensitive shipment information by controlling access based on the validity of the provided postal code.