Error: 502 Bad Gateway

Hello,
I am getting error 502 Bad Gateway on domain when i make sub directory and put there php file, when i use html no problem.
I dont know why but one some accounts what i have created i am not getting this problem. Only just on one and new accounts i tried to use same permissions like i have on accounts where is no problem with it but still same problem also i tried fix permissions and fix internal server error.
Thanks for help.

If you can run php files in the root folder, it's a permission issue.  Of you can't, php-fpm might not be running.