This combination gave me no documentation online, Recently Backuppc is available as SCGI Script version.
I did not had luck setting that up, as nginx lack documentation for scgi.

So let's get started, If you are here you might already know there is no packaged version of Backuppc 4.x available. I've decided to take shortcut and repackaged latest version available from fedora 27.

Once you install the package you should be good to go, configuration and all needed files are in place.

| Needed Packages

yum install -y BackupPC-4.1.5-1.el7.x86_64.rpm BackupPC-XS-0.57-1.el7.x86_64.rpm rsync-bpc-3.0.9.11-1.el7.x86_64.rpm nginx

| Needed CPAN Module

cpan install SCGI