dirname( __FILE__) returning wrong directory inside plugin

I resolved the issue by using $dir = plugins_url() . '/simple/acf/'; in step 2. I kept everything else the same.

// 2. Customize ACF dir
add_filter('acf/settings/dir', 'my_acf_settings_dir');

function my_acf_settings_dir( $dir ) { 
  // update path
  $dir = plugins_url() . '/simple/acf/';

  // return
  return $dir; 
}