IBM-CLOUD putting object with private ACL got a FULL_CONTROLL permission

Question

My main goal is to put an object in private mode

I'm using aws-sdk-php API to handle this case :

        $client->putObject(
            [
                'ACL'    => 'private',
                'Body'   => '...',
                'Bucket' => '...',
                'Key'    => '...'
            ]
        );

When executing, I get the error :

"Grants" => [
  0 => array:2 [
    "Grantee" => [
      "DisplayName" => "..."
      "ID" => "..."
      "Type" => "CanonicalUser"
    ]
    "Permission" => "FULL_CONTROL"
  ]
]

and I still can access it via a browser!

Any idea's help to resolve it would be thankful.