You have installed your BulldogOne and it has shown previously on the tracker app...
The BulldogOne has a sleep function to help preserve battery life. If no lights are showing but it is still connected to an external power supply, the tracker will be in sleep mode. When the tracker detects movement, the tracker will wake up and the lights will flash. Note that in sleep mode the tracker can still be controlled via the smartphone app.
You have installed your BulldogOne but has NOT previously shown on the tracker app...
Check the external power to the tracker is supplying between 12 and 24 Volts DC to the tracker. When power is connected correctly the red LED will illuminate and remain on.