ERROR: Cookies are blocked or not supported by your browser

It turns out I had DOMAIN_CURRENT_SITE set incorrectly in wp-config.php. (This particular install was a copy of another server, and the domain hadn’t fully been changed.)

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