When an aPower shows as "Offline" it means that it has no communication with the aGate. In this instance, as a homeowner your best course of action is to call your installer and have them inspect the communication lines for the system.
If you are a certified installer, this error will typically be accompanied by CAN communication errors of different types in the Warning section of your app when looking at a specific system. For this specific scenario, the first thing to do would be to confirm that the CAN lines are connected and that it's confirmed that they were terminated correctly via testing with a network line tester. If the issue persists, check the CAN ports for damage, take pictures, and reach out to the FranklinWH Service Line.