Class 'mPDF' not found in Yii2 - server

Question

I have problem with my page on server.
I'm using yii2 framework and mPDF;
All configured according to the instructions: http://www.bsourcecode.com/yiiframework2/create-pdf-files-using-mpdf-in-yiiframework-2-0/
Page work on localhost on Windows and Xampp
When I try run page on Debian 8 I have error:
Class 'mPDF' not found
Configuration: http://www.bsourcecode.com/yiiframework2/create-pdf-files-using-mpdf-in-yiiframework-2-0/
function in php:
public function actionCreatepdf()
{
$request = Yii::$app->request;
$generate_table = $request->post();
$mpdf = new mPDF;
$mpdf->WriteHTML($this->renderPartial('view_pdf', ['data'=>$data]));
$mpdf->Output('data.pdf', 'D');
exit;
}
I have no idea what I'm doing wrong, it's not running on Debian

Answer 1

I had this issue when migrating from Ubuntu (php 5.6) to CentOS 7 (PHP 7.1)
The easiest thing to do, without manually editing the composer file was to change the use/import in the controller:
//use mPDF; #Php 5.6
use Mpdf\Mpdf; #Php 7.0

Answer 2

Solved! As mentioned before it was due to capital cases.
I used following and it is now working on CENTOS 7 (probably similar on most Linux versions)
<?php
namespace app\controllers;
use Yii;
//use mPDF; Note this line is Commented out
use mpdf;
And then use it as follows:
public function actionIndex(){
$model = new Mpdf();
$model->SetHeader('header');
$model->WriteHTML("PDF contents");
$model->SetFooter('footer');
$model->Output('MyPDF.pdf', 'D');
exit;
}

Answer 3

In my case which i just resolved, adding
'mPDF\' => array($vendorDir . '/mpdf') to autoload_psr4.php required me to namespace most of the class files in ../mpdf/classes using the line
namespace mPDF;
Also among the errors i fixed was changing include to include_once to prevent php from seeing some classes as duplicate declaration despite the presence of class_exists() test