curl -X PUT \
 /public/checkout/cart/{id}/change-quantity \
 --header "Content-Type: application/json" \
 --header "Authorization: Bearer <token>" \
 --data '{
    "cartItemId": ""
}'

import requests

url = "https://coreapi.io/public/checkout/cart/{id}/change-quantity"

payload = {
    "quantity": 10,
    "cartItemId": "<string>"
}
headers = {
    "Authorization": "Bearer <token>",
    "Content-Type": "application/json"
}

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

print(response.text)

const options = {
  method: 'PUT',
  headers: {Authorization: 'Bearer <token>', 'Content-Type': 'application/json'},
  body: JSON.stringify({quantity: 10, cartItemId: '<string>'})
};

fetch('https://coreapi.io/public/checkout/cart/{id}/change-quantity', 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://coreapi.io/public/checkout/cart/{id}/change-quantity",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "PUT",
  CURLOPT_POSTFIELDS => json_encode([
    'quantity' => 10,
    'cartItemId' => '<string>'
  ]),
  CURLOPT_HTTPHEADER => [
    "Authorization: Bearer <token>",
    "Content-Type: application/json"
  ],
]);

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

curl_close($curl);

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

{
  "price": {
    "amountDue": 123,
    "currencyCode": "EUR",
    "netAmount": 123,
    "taxes": [
      {
        "netAmount": 123,
        "taxAmount": 123,
        "rate": 123
      }
    ],
    "discountDetails": [
      "<string>"
    ]
  },
  "id": "c1b0d0c0-0b0b-4b0b-8b0b-0b0b0b0b0b0b",
  "status": "open",
  "customer": "c1b0d0c0-0b0b-4b0b-8b0b-0b0b0b0b0b0b",
  "email": "<string>",
  "invoiceAddress": {
    "id": "<string>",
    "vatId": "DE123456789",
    "type": "TYPE_DEFAULT",
    "default": "true",
    "status": "active",
    "city": "Berlin",
    "zip": "12345",
    "street": "Musterstraße",
    "houseNumber": "1a",
    "countryCode": "DE",
    "companyName": "ACME Inc.",
    "salutation": "Herr",
    "addition": "c/o John Doe",
    "costCentre": "123456789",
    "firstName": "John",
    "lastName": "Doe"
  },
  "customerPrefill": {},
  "paymentMethod": "c1b0d0c0-0b0b-4b0b-8b0b-0b0b0b0b0b0b",
  "items": [
    {
      "id": "<string>",
      "name": "<string>",
      "description": "<string>",
      "quantity": 1,
      "quantityDetails": {
        "aggregationType": "count",
        "unit": "<string>",
        "description": "<string>",
        "quantityEditable": true
      },
      "price": {
        "currencyCode": "EUR",
        "taxRate": 123,
        "totalNetAmount": 10,
        "type": "recurring",
        "calculationType": "flat_fee",
        "payInAdvance": true,
        "price": {
          "amount": 123
        },
        "recurring": {
          "interval": "day",
          "intervalCount": 123,
          "trialPeriodDays": 123,
          "recurringAmount": 123
        },
        "freeUnits": 1
      },
      "type": "product",
      "periods": [
        {
          "contractPeriod": "<string>",
          "cancellationPeriod": "<string>"
        }
      ]
    }
  ],
  "completionDetails": [
    "<string>"
  ],
  "settings": {
    "allowCoupons": true,
    "forceCompany": true,
    "backButton": {
      "url": "https://example.com",
      "label": "Back to the shop"
    }
  }
}