Dediğim yöntemi uyguladım aldığım sonuç bu. Kodlar aşağıda yer alıyor. postman üzerinden php kodu denemeyin çoğu zaman yalan dolan gibi bir şey ya da biz yapamıyoruz (yüksek ihtimal biz yapamıyoruz)

<?php

$url = "http://api.cdek.com.tr:8090/CdekAPI/resources/remote/createDelivery";

$curl = curl_init($url);
curl_setopt($curl, CURLOPT_URL, $url);
curl_setopt($curl, CURLOPT_POST, true);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);

$headers = array(
    "params: {'userName':'TEST','function':'CREATE','date':'28.04.2022 09:09:09','signature':'E0EFEBC4F95C18908418E80F0666B04A'}",
   "Content-Type: application/json;charset=UTF-8",
);
curl_setopt($curl, CURLOPT_HTTPHEADER, $headers);

$data = <<<DATA
{
 "delivery" : {
 "hasCod" : false,
 "codAmount" : 0.0,
 "codCurrency" : "",
 "collect" : false,
 "descriptionOfContent" : "Rick And Morty Skecth Siyah Kapşonlu Sweatshirt / Hoodie Color: Siyah Size: L",
 "itemCurrency" : "TRY",
 "purchaseOrderNo" : "112028125995718",
 "receiver" : {
 "address" : {
 "addressLine1" : "Россия, Чувашская Республика, Чебоксары, Пролетарская улица",
"addressLine2" : "",
"city" : "Чебоксары",
"country" : {
 "code1" : "RU",
"code2" : "RUS",
"customsCode" : "75",
"name" : "Russia",
"name2" : "Russia",
"phoneCode" : "7"
 },
"region" : "ЧУВАШСКАЯ РЕСПУБЛИКА",
"zipCode" : "42380337"
 },
 "email" : "belova173226@mail.ru",
 "name1" : "Белова Анастасия",
 "name2" : "Belova Anastasiya",
 "name3" : "",
 "phone" : {
 "countryCode" : "RU",
"phoneNumber" : "9876753495"
 }
 },
 "recipientCountryName" : "Russia",
 "sender" : {
 "address" : {
 "addressLine1" : "ESENTEPE Mah. CEVİZLİ D-100 GÜNEY YANYOL Cad. KARTAL VİZYON Sit. D BLOK Apt. No: 13 / 83",
 "addressLine2" : "",
"city" : "İstanbul",
"country" : {
 "code1" : "TR",
"code2" : "TUR",
"customsCode" : "52",
"name" : "Turkey",
"name2" : "Turkey",
"phoneCode" : "90"
 },
"region" : "",
 "zipCode" : ""
 },
 "email" : "takdemir@logitransport.com",
 "name1" : "LOGİHUB DIŞ TİCARET ANONİM ŞİRKETİ",
 "name2" : "",
 "name3" : "",
 "phone" : {
 "countryCode" : "90",
"phoneNumber" : "216 660 17 70"
 }
 },
 "seller" : {
 "name1" : "Akif Bingül"
 }
 },
 "itemList" : [
 {
 "declaredValue" : 259.88,
 "description" : "Rick And Morty Skecth Siyah Kapşonlu Sweatshirt / Hoodie Color: Siyah Size: L",
 "descriptionUtf" : "Худи Rick And Morty Color: Siyah Size: L",
 "link" : "https://www.ozon.ru/context/detail/id/202969875",
 "quantity" : 1,
 "skuCode" : "126805860061",
 "hsCode" : "609000000121"

 }
 ]
 }
DATA;

curl_setopt($curl, CURLOPT_POSTFIELDS, $data);

//for debug only!
curl_setopt($curl, CURLOPT_SSL_VERIFYHOST, false);
curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, false);

echo $resp = curl_exec($curl);
curl_close($curl);