The DHL Shipment Tracking - Unified API is connected to multiple data sources from the different DHL divisions, but not all. This means that even though it covers a large range of DHL products and services, it doesn't cover all of them.
Consequently, it is possible that when querying a tracking ID that is not supported in any of our sources, the API will naturally return a 404 error.
DHL tracking IDs have many different string structures depending on the service, the country, and the division. The general scope of the services covered by the API is described in the documentation.
If your tracking ID starts with the following initials, it's not included in the API scope: A4, F1, LE, LR, LY, RJ, RS, RT, UQ, UR, UE, UF, UG, UU, QL.
Also, please note that there's an expected delay between the moment that a label is created and the time the new shipment appears in the digital systems. Additionally, tracking IDs are systematically purged from the database, most after 4 months but some services like "Internetmarke" from Post and Parcel Germany after 21 days.
Please excuse any inconvenience, we are constantly working to improve the coverage of the DHL Shipment Tracking - Unified API.