I tried it, but I seem to do something wrong.

I simply took the example from the documentation but simply get a 0 byte file. I will continue investigating, but maybe someone of you has some information what might be wrong?

This is what I have in my Dancer route:

content_type 'application/vnd.ms-excel';
my $buffer;
open my $fh, '>', \$buffer;
my $workbook  = Spreadsheet::WriteExcel->new($fh);
my $worksheet = $workbook->add_worksheet();
#  Add and define a format
my $format = $workbook->add_format(); # Add a format
$format->set_bold();
$format->set_color('red');
$format->set_align('center');
        
# Write a formatted and unformatted string, row and column notation.
my $col = 0;
my $row = 0;
$worksheet->write($row, $col, 'Hi Excel!', $format);
$worksheet->write(1,    $col, 'Hi Excel!');
        
# Write a number and a formula using A1 notation
$worksheet->write('A3', 1.2345);
$worksheet->write('A4', '=SIN(PI()/4)');
close $fh;
return $buffer;
[download]

Found the mistake
I forgot $workbook->close();.