[Solved] Problem on save image in public directory

I have the structure below my project:

(private directories)

/home/my_project/App/Controllers/Api/V1/FileController.php

(public directories)

/home/public_html/my_site/assets/images

I'm trying to send an Api file to the / images directory with file_put_contents but I'm not getting it. I've tried with:
file_put_contents (FCPATH. '....');
file_put_contents (APPPATH. '....');
file_put_contents (ROOT. '....');
file_put_contents (__ DIR__. '....');

I tried to change the permissions of the directory from 755 to 777.

And nothing worked.
What is the correct way to do this?