How to print more than one checkbox in MPDF

I am new on PHP and I would like to know how can I print more than one checkbox (values) in MPDF

Here is my HTML code with one checkbox:

<div class="primary-checkbox">
     <input name='checkboxName[]' value='Behaviour Analysis' type="checkbox" id="second-checkbox">
         <label for="second-checkbox"></label>
</div>

Here is in PHP to print all the values (is working well):

foreach($_POST['checkboxName'] as $value){ echo "Checked values: ".$value;}

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And here is $mpdf->WriteHTML (is printing only ONE checkbox (value)):

$mpdf->WriteHTML('<h3>Use Case Type<br /></h3>' . $value .');

enter image description here

What is the easiest way to print all the checkboxes (values) in $mpdf->WriteHTML, Any help please, thanks?