Error after Checkout - Try to install E-Tickets with HikaSerial

<?php echo JHTML::_('select.genericlist', $fonts, $map.'[font]', 'class="custom-select"', 'value', 'text', @$text['font'], 'attserial_fonts_' . $i); ?><br/>

<?php echo JHTML::_('select.genericlist', $fonts, $map.'[font]', 'class="custom-select"', 'value', 'text', @$text['font'], 'attserial_fonts_' . $i); ?><br/>
<label><input type="checkbox" name="<?php echo $map ?>[font_attr][]" value="b" <?php echo (in_array($text['font_attr'] ?? [], 'b')) ? 'checked="checked"' : ''; ?>/> Bold</label> 
<label><input type="checkbox" name="<?php echo $map ?>[font_attr][]" value="i" <?php echo (in_array($text['font_attr'] ?? [], 'i')) ? 'checked="checked"' : ''; ?>/> Italic</label> 
<label><input type="checkbox" name="<?php echo $map ?>[font_attr][]" value="u" <?php echo (in_array($text['font_attr'] ?? [], 'u')) ? 'checked="checked"' : ''; ?>/> Underline</label> 

$pdf->SetFont($font, '', (int)$d['size']);

$font_attr = '';
if(!empty($d['font_attr'])) {
	$font_attr = array_intersect($d['font_attr'], array('b','i','u'));
	$font_attr = strtoupper(implode('', $font_attr));
}
$pdf->SetFont($font, $font_attr, (int)$d['size']);

'font' => @$text['font']

'font' => @$text['font'],
'font_attr' => @$text['font_attr'],