nginx plugin centos

Most probably, $PATH for root and your user account differ

Above info it's obtained with root, it's the only account on this test box:

[root@ajenti /]# echo $PATH
/usr/lib64/ccache:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/root/bin:/root/bin

[root@ajenti /]# which nginx
/usr/local/sbin/nginx

Sorry, but we only support distribution-packages nginx, one which employs /etc/nginx/sites-available.d config layout. If you believe your nginx build does the same, you might want to try and symlink it into /usr/bin