“www” as the owner of php file and nginx process, the script still cannot write?

I am using a “duplicator” plugin on wordpress and required to configure the folder wp-snapshots, wp-snapshots/tmp to the owner of the php running process and I did.

Both folder and all files under are owned by “www”. Nginx is run by “www”. But I still can’t pass the permission check.

I run “whoami” in a php scirpt to have confirmed the php script is running by www. So what’s wrong?

Normally I just set the folder to 777 but I got fed up with this permission why thing. It happens all the time. What’s wrong??

Thanks!