How to add an object parameter into a string post api curl? - php

Question

Can someone help me to fix this issue, i need to provide an object type parameter to my code to fetch data using shopee API.
here is my code
$partner_key = "c423d22ccf4a8f1ca3cf9f49d7995f7d2a11e58b6a57036bd8385e8d978b4db2";
$partner_id = 2003151;
$shop_id = 30334567;
$ordersn = "";
$username = "info#pollandhopia.com";
$password = "101382qpqeiw";
$datenow = time();
$parcel->item_id = 455371271;
$parcel->variation_id = 0;
$parcel->order_item_id = 455371271;
$parcel->promotion_group_id = 0;
$object = json_encode($parcel);
$post = '{
"shopid": '.$shop_id.',
"ordersn": "220506EWDX3UXW",
"partner_id": '.$partner_id.',
"timestamp": '.$datenow.',
"parcels": '.$parcel.'
}';
$url = "https://partner.shopeemobile.com/api/v1/orders/split";
//Generate a signature base string for POST
$base_string = $url."|".$post;
//Generate a unique signature
$signature = hash_hmac('sha256', $base_string, $partner_key);
#echo $signature.'----'.$datenow.'-'.$object;exit;
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_POST,1);
curl_setopt($ch, CURLOPT_POSTFIELDS, $post);
curl_setopt($ch, CURLOPT_USERPWD, "$username:$password");
curl_setopt($ch, CURLOPT_HTTPAUTH, CURLAUTH_ANY);
curl_setopt($ch, CURLOPT_HTTPHEADER, array("Authorization:".$signature, "Content-Type: application/json"));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$result = curl_exec($ch);
$result = json_decode($result);
curl_close($ch);
Then the documentation params is here
Here is my error:
An uncaught Exception was encountered
Type: Error
Message: Object of class stdClass could not be converted to string