curl --request POST \
  --url https://api.example.com/api/storefront/cart/{cart_id}/items \
  --header 'Content-Type: application/json' \
  --header 'X-Site-ID: <x-site-id>' \
  --data '
{
  "variant_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "quantity": 1
}
'

import requests

url = "https://api.example.com/api/storefront/cart/{cart_id}/items"

payload = {
    "variant_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
    "quantity": 1
}
headers = {
    "X-Site-ID": "<x-site-id>",
    "Content-Type": "application/json"
}

response = requests.post(url, json=payload, headers=headers)

print(response.text)

const options = {
  method: 'POST',
  headers: {'X-Site-ID': '<x-site-id>', 'Content-Type': 'application/json'},
  body: JSON.stringify({variant_id: '3c90c3cc-0d44-4b50-8888-8dd25736052a', quantity: 1})
};

fetch('https://api.example.com/api/storefront/cart/{cart_id}/items', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.example.com/api/storefront/cart/{cart_id}/items",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "POST",
  CURLOPT_POSTFIELDS => json_encode([
    'variant_id' => '3c90c3cc-0d44-4b50-8888-8dd25736052a',
    'quantity' => 1
  ]),
  CURLOPT_HTTPHEADER => [
    "Content-Type: application/json",
    "X-Site-ID: <x-site-id>"
  ],
]);

$response = curl_exec($curl);
$err = curl_error($curl);

curl_close($curl);

if ($err) {
  echo "cURL Error #:" . $err;
} else {
  echo $response;
}

package main

import (
	"fmt"
	"strings"
	"net/http"
	"io"
)

func main() {

	url := "https://api.example.com/api/storefront/cart/{cart_id}/items"

	payload := strings.NewReader("{\n  \"variant_id\": \"3c90c3cc-0d44-4b50-8888-8dd25736052a\",\n  \"quantity\": 1\n}")

	req, _ := http.NewRequest("POST", url, payload)

	req.Header.Add("X-Site-ID", "<x-site-id>")
	req.Header.Add("Content-Type", "application/json")

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(string(body))

}

HttpResponse<String> response = Unirest.post("https://api.example.com/api/storefront/cart/{cart_id}/items")
  .header("X-Site-ID", "<x-site-id>")
  .header("Content-Type", "application/json")
  .body("{\n  \"variant_id\": \"3c90c3cc-0d44-4b50-8888-8dd25736052a\",\n  \"quantity\": 1\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://api.example.com/api/storefront/cart/{cart_id}/items")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true

request = Net::HTTP::Post.new(url)
request["X-Site-ID"] = '<x-site-id>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"variant_id\": \"3c90c3cc-0d44-4b50-8888-8dd25736052a\",\n  \"quantity\": 1\n}"

response = http.request(request)
puts response.read_body

{
  "id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "items": [
    {
      "id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
      "variant_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
      "product_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
      "product_name": "<string>",
      "variant_name": "<string>",
      "sku": "<string>",
      "image_url": "<string>",
      "price": "<string>",
      "quantity": 123,
      "total": "<string>"
    }
  ],
  "subtotal": "<string>",
  "items_count": 123,
  "created_at": "2023-11-07T05:31:56Z",
  "updated_at": "2023-11-07T05:31:56Z"
}

{
  "detail": [
    {
      "loc": [
        "<string>"
      ],
      "msg": "<string>",
      "type": "<string>",
      "input": "<unknown>",
      "ctx": {}
    }
  ]
}