Cookie not created in AJAX request

Use COOKIEPATH and COOKIE_DOMAIN constants.

setcookie( 'welcomeback', ucfirst( $_POST['firstname'] ), strtotime( '27 Feb 2017' ), COOKIEPATH, COOKIE_DOMAIN );

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