$filename = DELIVERY_LABEL_GENERATOR_PLUGIN_DIR . '/assets/output-file.csv';

  // clean out other output buffers
  //$fp = fopen( $filename, 'w' );
  ob_start();
  $fp = fopen( 'php://output', 'w' ) or show_error("Can't open php://output");

  //Creates the header row. Uses tab as a seperator
  $header_row = array_keys( $final_data[0] );
  fputcsv( $fp, $header_row, "," );

  //Maps the data row with the columns headers.
  foreach( $final_data as $row ) {
   fputcsv($fp, $row,",");
  }
  //fclose($fp); To see how data is handled, pay attention what happens to '$csvStr;'
  fclose($fp) or show_error("Can't close php://output");
  $csvStr = ob_get_contents();
  ob_end_clean();

  //Generates url to access the final file.
  $output_file_url = DELIVERY_LABEL_GENERATOR_PLUGIN_URL . '/assets/output-file.csv';
  /*$output_file = "<p id='nt-download-link'>
       <a href='$output_file_url'>" .
        __( 'Download the output file by clicking here', 'nt-delivery-label-generator') .
       "</a>
      </p>";*/
  $output_file = $csvStr;
  $data = array(
   'data' => __( 'Thank you for sending us your feedback', 'nt-delivery-label-generator' ),
   'output_file' => $output_file
  );
  wp_send_json_success( $data, 200 );
  exit();