I tried to build a hash out of a an EXCEL CSV file using JKeenan's Text::CSV::Hashify, but I can't get it work.

use strict;
use warnings;
use Text::CSV::Hashify;

my $obj = Text::CSV::Hashify->new( {
        file => './data/BuildHash.csv',
        format => 'hoh',
        key => 'A',
        });
        
print my $hash_ref = $obj -> fields;
[download]

The message returned is: Key ' ' already seen at ...

I tried to declare coloumn A as key. The first coloumn of the CSV file consists of fields with unique IDs. How can I declare this coloumn as key?