Service Call, Electrician Tries to Install his 1st Doorbell, but doesn’t go to plan, Thoughts?

What happens here

This video documents an electrician's attempt to install a new smart doorbell. After installation, the doorbell repeatedly turned on for 30 seconds and then off, indicating an issue. The electrician troubleshoots by checking the voltage at the doorbell transformer, the traditional chime, and the smart doorbell itself. He discovers a significant voltage drop (from 18V at the transformer to 10V at the doorbell), which is causing the smart doorbell to malfunction. The video concludes with the electrician seeking advice on how to resolve this electrical issue without incurring further costs.