They say any character combination is a valid Perl code. But it's not true. There's no sigil combination like %@. You are interested in a scalar value, so use $chaseArray[$month]{Shopify}.

Also, to extract the month from the horribly MM/DD/YYYY formatted date, you need to tell substr to use 2 characters.

Here's an example that actually does something:

#!/usr/bin/perl
use strict;
use warnings;
use Text::CSV_XS;


my $chaseCSV = 'Text::CSV_XS'->new ({ binary => 1 });
my $inFile = *DATA;

my @chaseArray;
while (my $row = $chaseCSV->getline($inFile)) {

    my @chaseList = @$row;
    my $month = substr $chaseList[1], 0, 2;

    if ($chaseList[2] =~ /(Paypal|Etsy)/) {
        my $company = $1;
        my $temp = $chaseList[3] + ($chaseArray[$month]{$company} // 0
+);
        $chaseArray[$month]{$company} = $temp;
    }
}

use Data::Dumper;
print Dumper \@chaseArray;

__DATA__
Debit,01/06/2024,Paypal paymemnt, 25.25,debit_card
Debit,01/09/2024,Paypal paymemnt, 10.13,debit_card
Debit,03/15/2024,Etsy paymemnt, 52.23,debit_card
Debit,03/22/2024,Paypal paymemnt, 16.52,debit_card
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The output:

$VAR1 = [
          undef,
          {
            'Paypal' => '35.38'
          },
          undef,
          {
            'Paypal' => '16.52',
            'Etsy' => '52.23'
          }
        ];
[download]