We use the GPS in your BlueLink Hardware and your truck's odometer to record IFTA, so there are a few reasons why they may not be calculating perfectly.
1. The Driver isn't using the ELD correctly. If a driver isn't actually connecting to the ELD hardware through bluetooth from their mobile device or tablet you will not receive IFTA miles for that driver. This is because without connection to the hardware we have no way of receiving the GPS locations. Inside their app, have your driver go to Settings > ELD Connect and connect to their Bluelink hardware which should be attached to the diagnostic port of their truck.
2. Your Bluelink ELD hardware isn't picking up engine events due to incorrect settings. The bluelink hardware comes with default settings best matched to your vehicle connection type. However, every vehicle is different and may require settings to be modified on the actual hardware device in order to accurately pickup the engine activity. If you suspect this is the issue you will need to adjust the settings.
3. Your Bluelink ELD hardware wasn't receiving GPS signal for a prolonged period of time. The Bluelink hardware is very good at receiving signal but there are some situations where it may not be able to receive one if it is sufficiently blocked (e.g. mounted under the dash). Make sure your ELD hardware is positioned on the dash or in a place where it has a direct view to the sky for best satellite communication.