Two of the main reasons are either technical or timing reasons.
Technical reasons are because telephony systems, communication platforms, and dialers are inherently different technologies from the networks and therefore have access to different data points.
Placing a call is a complicated process starting with the user interface, going through a device, calling from an originating service provider and then ending with the terminating service provider (TSP). Branding takes place on the TSP, and that is what is considered a call. If the call terminates before then, the TSP might have no way of knowing if a call was attempted to begin with.
In the case of call centers making large volumes of calls, there is a high likelihood those counts are going to be different.
Timing can also be a reason. Because of the time it takes to get TSP data from partners and integrate that into the First Orion Customer Portal reports, it can take up to 48 hours for calls to be accurately reported across all networks.
However, First Orion reports back only calls that successfully delivered branding.