The voltage required for the Video Doorbell is 10-24 Vac.
Check the voltage at the transformer. Typically for a standard 16V transformer it will read ~19-20 Vac.
Check the voltage at the Doorbell. This is typically ~2V less than at the transformer.
If you are not getting any voltage reading at the doorbell, then that means there is a disconnect or “short” somewhere in the wiring. This will need to be diagnosed by an electrician.