The usage from the SYNOPSIS is when you have a bin and lib sitting next to each other, e.g. in a typical CPAN distribution. In your case, that would be:

use FindBin qw($Bin);
use lib "$Bin/flies/lib";
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$Bin is the directory where your Perl script started. Have a look at the edge cases in FindBin whether you need FindBin::again or $FindBin::RealBin, but I guess it will already work as given. I apologize for having used a misleading CPAN link in my first post: FindBin is in Perl core.