There are a few reasons you could be experiencing this.
Even though you have activated your SpotOn collar, you have not subscribed to the cellular service. To subscribe, click here.
The collar is off - turn it on and it should connect.
The collar is on but it has a poor connection or doesn’t have cellular service.
If you have subscribed to the cellular plan and you have no service, your dog (and collar) is likely in an area with poor AT&T/T-Mobile cell service. As your dog moves around your property it will continue to try connecting to the closest AT&T/T-Mobile cell towers. Note even though SpotOn uses AT&T and T-Mobile 3G networks (not Verizon), it will still communicate with your phone regardless of which cell carrier you use (just like you can call your mom even though you use AT&T and she has MetroPCS).