Perhaps the seller gave you a link to a "fake" service and sent the parcel by regular mail WITHOUT the possibility of real tracking. On some online stores, for example, on AliExpress, the seller is obliged to give the buyer a tracking number for the parcel.
As a rule, the issued track really starts to be "tracked", but only on this "strange" website. It looks quite reliable and the buyer may not even have any doubts. In most cases, the statuses on such services are generated according to similar rules for all tracks of this service, differing only in dates. The intervals between events coincide with an accuracy of +- 1 day. The texts and the sequence of events also coincide. But in reality, the parcel, if of course it was sent, may not arrive or "get stuck" on the way. Although, according to the statuses from the "fake" service, everything is fine, the parcel is "on the way". These sites are created specifically to deceive buyers. And only for this.
At numerous requests from application users, "support" for fake services has been added. But the TrackChecker application is designed to track shipments on real services, and if the service is not one, then when you select it, you will see a corresponding warning.