One thing that has helped me in similar situations was to change into the directory containing the files of interest. For example, note the tiny changes to your code:

use strict;
use warnings;
use Data::Dumper qw(Dumper);
use File::Spec;
use Digest::SHA qw(sha256_hex);

print join("\n", @ARGV),"\n\n";
#print Dumper \@ARGV;

my $dir = $ARGV[0];
my $url = $ARGV[1];

my @array;
opendir DIR, $dir or die "cannot open dir $dir: $!";
chdir $dir;                                          #  added chdir
while(my $file = readdir DIR) {
    next unless -f $file;                            #  simplified fil
+e check
    next if($file =~ m/^\./);                        #  removed quotes
    print "${\File::Spec->rel2abs($file)}\n";

    my %hash = (
        path    =>  File::Spec->rel2abs($file),
        size    =>  -s $file,
        id      =>  sha256_hex($file),
    );

    push(@array, \%hash);
}
closedir DIR;

print Dumper sort \@array;
[download]

Hope it works out for you!

--Derrick