如何修复'require_once()无法打开流'

I'm making a website and I have to access the init file which is in the core folder. I'm currently in the includes folder detailsmodal.php file which is being triggered by an onclick event. The path I used

require_once './core/init.php';

is giving errors when i click on the modal:

Warning: require_once(./core/init.php): failed to open stream: No such file or directory in C:\xampp\htdocs\mednew\includes\detailsmodal.php on line 2

Fatal error: require_once(): Failed opening required './core/init.php' (include_path='C:\xampp\php\PEAR') in C:\xampp\htdocs\mednew\includes\detailsmodal.php on line 2

https://gyazo.com/e17324da3caa48c342255bb4bfd1344d

require_once('../../core/init.php');

I think you got two directories ahead instead of one.