How to add multiple product gallery images from front-end

-I am running a woo commencers shop

-Users have the ability to add products using wp insert post

-The product gallery multiple image upload will only add the last image to the post but in media they are all attached to the correct post

This is my code

function.php

function my_handle_attachment($file_handler,$post_id,$set_thu=false) {
  if ($_FILES[$file_handler]['error'] !== UPLOAD_ERR_OK) __return_false();

  require_once(ABSPATH . "wp-admin" . '/includes/image.php');
  require_once(ABSPATH . "wp-admin" . '/includes/file.php');
  require_once(ABSPATH . "wp-admin" . '/includes/media.php');

  $attach_id = media_handle_upload( $file_handler, $post_id );

  if ( is_numeric( $attach_id ) ) {

    update_post_meta( $post_id, '_product_image_gallery', $attach_id );

  }
  return $attach_id;  
}

front-end

if ( $_FILES ) { 
        $files = $_FILES["my_file_upload"];  

        foreach ($files['name'] as $key => $value) {      

                if ($files['name'][$key]) { 

                    $file = array( 
                        'name' => $files['name'][$key],
                        'type' => $files['type'][$key], 
                        'tmp_name' => $files['tmp_name'][$key], 
                        'error' => $files['error'][$key],
                        'size' => $files['size'][$key]
                    ); 
                    $_FILES = array ("my_file_upload" => $file); 

                    $newupload = my_handle_attachment( "my_file_upload", $post_id);


                } 

            } 

    }

input

<input type="file" name="my_file_upload[]" multiple="multiple" >

This will upload all images and attach them to the correct post but only the last image will show up in Products gallery image section. What am i doing wrong?

if ( ! empty( $_FILES['muti_files'] )  ) {
            $files = $_FILES['muti_files'];
            foreach ($files['name'] as $key => $value){
                if ($files['name'][$key]){
                    $file = array(
                    'name' => $files['name'][$key],
                    'type' => $files['type'][$key],
                    'tmp_name' => $files['tmp_name'][$key],
                    'error' => $files['error'][$key],
                    'size' => $files['size'][$key]
                    );
                }
                $_FILES = array("muti_files" => $file);
                $i=1;
                    foreach ($_FILES as $file => $array) {
                          if ($_FILES[$file]['error'] !== UPLOAD_ERR_OK) __return_false();
                            require_once(ABSPATH . "wp-admin" . '/includes/image.php');
                            require_once(ABSPATH . "wp-admin" . '/includes/file.php');
                            require_once(ABSPATH . "wp-admin" . '/includes/media.php');
                            $attachment_id = media_handle_upload($file, $post_id);
                            $vv .= $attachment_id . ",";
                            $i++;
                    }
                    update_post_meta($post_id, '_product_image_gallery',  $vv);
            }
        }