If you have a hash of hashes (HoH), such as you have here, then you need to recurse through each level accordingly. The comma separator won't cut it. Here's a quick reference:

foreach my $key (keys %hash)
{
     foreach my $subkey (keys %{$hash{$key}})
     {
          print "$key,$subkey => $hash{$key}{$subkey}\n";
     }
}
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This presumes you have a pure HoH structure, which is a fairly safe assumption if you've created it yourself. Note that in the second foreach you're casting the hash entry $hash{$key} as a hash itself so you can access the keys and iterate through this second layer.