AttributeError: ‘str’ object has no attribute ‘qty’

I am trying to post data to api of website using this code:

$url = 'apiurl';
$http = Http::withHeaders(['Content-Type' => 'application/json','Authorization' => 'token mytoken','Accept' => 'application/json'])->post($url, [
            "doctype"=> "Sales",
            "customer"=> "Dummy",
            "docstatus" => 0,
            "title"=> "title",
            "contact_display"=> "Dummy",
            "currency"=> "PHP",
            "order_type"=> "Sales",
            "delivery_date"=> "2022-10-12",
            "items" => [
                "item_code"=> "it",
                "item_name"=> "item",
                "qty"=> 1,
                "rate"=> "10.00",
                "doctype"=> "Sales Item",
                "docstatus"=> "0"
                
            ],
        ]);

But I keep getting this error:

{"exception":"AttributeError: 'str' object has no attribute 'qty'","exc":"["Traceback (most recent call last):\n File \"apps/frappe/frappe/app.py\",