how to upload the image in registeration page

Hi ,
i created one custom field :
<input type="file" class="woocommerce-Input woocommerce-Input--text " name="gst-file">

To store the image in wp_usermeta table am using following code:

$r = wp_handle_upload( $_FILES[‘gst-file’]);
update_user_meta( $user_id, ‘gst-file’, $r );

But the value is storing as follow:
a:1:{s:5:”error”;s:24:”Invalid form submission.”;}

The page I need help with: [log in to see the link]