Hello.
For such generic digits-only tracking numbers you should either provide exact carrier id (ds parameter for createTrack call) or at least country code (destCountry parameter). That’s because there are too many different local carriers with such digits-only numbers.
When you track such numbers on the website we guess that visitor from certain country most likely has tracking number from some local carrier from his country.
For API calls we can’t use such heuristic. So API users should use one or both parameters mentioned above.