如何在html2pdf（codeigniter）中修复非对象的prepend_child？

I'm trying to use HTML2PDF to print a PDF page that is created with HTML with all its CSS.

I used it inside an AJAX request, to have the print after clicking on a button. On the controller I implemented it in this way:

$this->load->library('html2pdf');
$this->html2pdf->folder('assest__/pdfs/');
$this->html2pdf->filename('printpage.pdf');
$this->html2pdf->paper('a4', 'portrait');
$this->html2pdf->html($view);
$this->html2pdf->create('download');

But I'm getting this kind of error:

Call to a member function prepend_child() on a non object

This kind of function is used in frame_tree.cls.php file. Whenever I try to print the $frame to which I apply the function it doesn't seem to be empty or null.

Here is what logs print_r($frame):

enter image description here

How can I solve this issue?

I am using mpdf, with inline CSS for each, and my framework is CodeIgniter, here is what I do:

  1. I prepared one HTML template that will contain the information I need,

  2. I used cURL to read that template, because am passing the parameters to it to generate the output.

  3. I passed the text to mpdf, and done.