get_the_post_thumbnail not working inside wp_get_nav_menu_items hook

That’s because object properties are case sensitive, thus $post->ID is not the same as $post->id .

Just by printing out these two you’ll notice the difference, or do a print_r of the $post object to see all of the available properties and methods.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)