Upload excel file to phpmysql error

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Hello guys I am going to upload my excel to sql but while i upload i get this error
Notice: Only variables should be passed by reference in C:\wamp64\www\invoic4\index.php on line 6

and this is index.php file

<?php
$connect = mysqli_connect("localhost", "root", "", "invoice4");
$output = '';
if(isset($_POST["import"]))
{
 $extension = end(explode(".", $_FILES["excel"]["name"])); // For getting Extension of selected file
 $allowed_extension = array("xls", "xlsx", "csv"); //allowed extension
 if(in_array($extension, $allowed_extension)) //check selected file extension is present in allowed extension array
 {
  $file = $_FILES["excel"]["tmp_name"]; // getting temporary source of excel file
  include("PHPExcel/IOFactory.php"); // Add PHPExcel Library in this code
  $objPHPExcel = PHPExcel_IOFactory::load($file); // create object of PHPExcel library by using load() method and in load method define path of selected file

  $output .= "Data Inserted<br>";
  foreach ($objPHPExcel->getWorksheetIterator() as $worksheet)
  {
   $highestRow = $worksheet->getHighestRow();
   for($row=2; $row<=$highestRow; $row++)
   {
    $output .= "";
    $docno = mysqli_real_escape_string($connect, $worksheet->getCellByColumnAndRow(0, $row)->getValue());
    $importaction = mysqli_real_escape_string($connect, $worksheet->getCellByColumnAndRow(1, $row)->getValue());
    $query = "INSERT INTO invoice_table(docno, importaction) VALUES ('".$docno."', '".$importaction."')";
    mysqli_query($connect, $query);
    $output .= '';
    $output .= '';
    $output .= '';
   }
  } 
  $output .= '<table class="table table-bordered"><tbody><tr><td>'.$docno.'</td><td>'.$importaction.'</td></tr></tbody></table>';

 }
 else
 {
  $output = 'Invalid File'; //if non excel file then
 }
}
?>


 
  <title>Import Excel to Mysql using PHPExcel in PHP
  
  
    
  body
  {
   margin:0;
   padding:0;
   background-color:#f1f1f1;
  }
  .box
  {
   width:1100px;
   border:1px solid #ccc;
   background-color:#fff;
   border-radius:5px;
   margin-top:100px;
  }
  
  
 
 
  <div class="container box">
   <h3 align="center">Import Excel to Mysql using PHPExcel in PHP</h3><br>
   
    Select Excel File
    
    <br>
    
   
   <br>
   <br>
   <?php
   echo $output;
   ?>
  </div>

What I have tried:

I do not know that is wrong with line 6