Codeigniter redirect issue with https - .htaccess

Question

I'm adding a pdf function to my project, but I have a strange issue with redirecting the function after it is completed.
initially, it works well on localhost and on a test host not using ssl certificate, but it is not working on the domain associated with ssl certificate I don't know the reason and no debugging info can guide me when I should start.
The working code with no ssl : http://idev-inc.com/lab/rwahl.com/invoice
You have to book hotel to get the link works with you otherwise it will rediect you to the homepage.
The same function and repo at this url : https://rwahl.com/ndmilestone/invoice
I looked for the most threads about redirection with ssl and I updated the
.htaccessto the following :
RewriteEngine on
# Enforce SSL https://www.
RewriteCond %{HTTPS} !=on
RewriteRule ^.*$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
###
# Removes access to the system folder by users.
# Additionally this will allow you to create a System.php controller,
# previously this would not have been possible.
# 'system' can be replaced if you have renamed your system folder.
RewriteCond %{REQUEST_URI} ^system.*
RewriteRule ^(.*)$ /index.php/$1 [L]
# Checks to see if the user is attempting to access a valid file,
# such as an image or css document, if this isn't true it sends the
# request to index.php
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
#####RewriteRule ^(.*)$ /ndmilestone/index.php/$1 [L]
RewriteRule ^(.*)$ /ndmilestone/index.php?/$1 [L,QSA]
I'm using mpdf library to generate the pdf files , And this is the invoice_as_pdf function :
function invoice_as_pdf(){
$assumptiondata=Array();
$filename="invoice".time().rand(1,9);
// As PDF creation takes a bit of memory, we're saving the created file in
// /downloads/reports/
$sub_folder="downloads/reports/$filename.pdf";
$pdfFilePath = FCPATH."/".$sub_folder;
$finalurl=base_url().$sub_folder;
// pass data to the view
if (file_exists($pdfFilePath) == FALSE){
ini_set('memory_limit','32M'); // boost the memory limit if it's low ;)
$this->theme->view('Admin/modules/global/invoice', $this->data, $this);
$html = $this->load->view('Admin/modules/global/idev_invoice_print', $data, true); // render the view into HTML
$this->load->library('pdf');
$mpdf = $this->pdf->load();
$mpdf=new mPDF('utf-8');
// $pdf->useAdobeCJK = true;
$mpdf->charset_in='UTF-8';
// Add a footer for good measure ;)
$mpdf->SetFooter($_SERVER['HTTP_HOST'].'|{PAGENO}|'.date(DATE_RFC822));
$mpdf->SetDirectionality('rtl');
$mpdf=new mPDF('ar','A4','','',32,25,27,25,16,13);
$mpdf->SetDirectionality('rtl');
$mpdf->mirrorMargins = true;
$mpdf->WriteHTML($html); // write the HTML into the PDF
$mpdf->Output($pdfFilePath, 'F'); // save to file because we can
}
$this->load->helper('url'); // it is auto-loaded but I'm testing to call here also
redirect($finalurl); //redirect to the new PDF
}
The pdf files are generated successfully also, actually I tried several scenarios but till now I couldn't get the reason for that.
Thanks in advance.