Preview url not working outside wp-admin

So, I created a link in the frontend which allows the user to preview their post. However, when I click on it, it takes me to the published post instead of previewing the changes I made.

Here is what I wrote:

a href=?php echo get_preview_post_link($post-ID) ? target=wp-preview-?php echo $post-ID ? id=post-preview Preview /a

If I go into wp-admin and preview the post, it works fine.