The most common reasons for not receiving responses for some of the vessels that belong to your fleets are:
Incorrect or No use of the timespan
- The API returns responses based on whether the information about a vessel was received during the defined /timespan:{value}/. If the timespan is not defined (default values is used) or is smaller than the time the AIS message was received then it is not contained in the API response.
No coverage in the area
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some of the vessels of your fleets may sail in areas with limited coverage from terrestrial or Satellite or roaming ais receiving stations.