https://www.youtube.com/watch?v=b4qSzYK2kFw&t=284. He doesn't knock on the front door until 8:58, after he has entered the exterior property and gone completely around the house knocking on windows/sliding doors. It's not until 16:25 that he finally calls out her name and identifies himself as a police officer and asks her to "make herself known."
Only after going completely around the house and into the back yard of the property and knocking on windows/sliding doors does the officer call Shannann's number (14:14).
Clearly permission is not needed to enter a gated/fenced yard on a welfare check. I don't know why this has become such a point of contention.