Video doorbell won’t run off mains

Hi I installed my video doorbell yesterday and hooked it up to the existing doorbell wires as per the instructions. However, it says in the device health it is running off battery and not receiving mains power which also means my existing bell doesn’t ring when the button is pressed. I’ve double checked the wires are secured okay. Does anyone have any ideas? Do I need the power kit to install in my existing bell? Thanks