curl --request POST \
  --url {protocol}://{host}/wp-json/cocart/v1/add-item \
  --header 'Content-Type: application/json' \
  --data '
{
  "quantity": "1",
  "product_id": "<string>",
  "variation_id": 123,
  "variation": {},
  "cart_item_data": {},
  "return_cart": false
}
'

import requests

url = "{protocol}://{host}/wp-json/cocart/v1/add-item"

payload = {
    "quantity": "1",
    "product_id": "<string>",
    "variation_id": 123,
    "variation": {},
    "cart_item_data": {},
    "return_cart": False
}
headers = {"Content-Type": "application/json"}

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

print(response.text)

const options = {
  method: 'POST',
  headers: {'Content-Type': 'application/json'},
  body: JSON.stringify({
    quantity: '1',
    product_id: '<string>',
    variation_id: 123,
    variation: {},
    cart_item_data: {},
    return_cart: false
  })
};

fetch('{protocol}://{host}/wp-json/cocart/v1/add-item', 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 => "{protocol}://{host}/wp-json/cocart/v1/add-item",
  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([
    'quantity' => '1',
    'product_id' => '<string>',
    'variation_id' => 123,
    'variation' => [
        
    ],
    'cart_item_data' => [
        
    ],
    'return_cart' => false
  ]),
  CURLOPT_HTTPHEADER => [
    "Content-Type: application/json"
  ],
]);

$response = curl_exec($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 := "{protocol}://{host}/wp-json/cocart/v1/add-item"

	payload := strings.NewReader("{\n  \"quantity\": \"1\",\n  \"product_id\": \"<string>\",\n  \"variation_id\": 123,\n  \"variation\": {},\n  \"cart_item_data\": {},\n  \"return_cart\": false\n}")

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

	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("{protocol}://{host}/wp-json/cocart/v1/add-item")
  .header("Content-Type", "application/json")
  .body("{\n  \"quantity\": \"1\",\n  \"product_id\": \"<string>\",\n  \"variation_id\": 123,\n  \"variation\": {},\n  \"cart_item_data\": {},\n  \"return_cart\": false\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("{protocol}://{host}/wp-json/cocart/v1/add-item")

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

request = Net::HTTP::Post.new(url)
request["Content-Type"] = 'application/json'
request.body = "{\n  \"quantity\": \"1\",\n  \"product_id\": \"<string>\",\n  \"variation_id\": 123,\n  \"variation\": {},\n  \"cart_item_data\": {},\n  \"return_cart\": false\n}"

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

{
  "key": "<string>",
  "product_id": 123,
  "variation_id": 123,
  "variation": {},
  "quantity": 123,
  "data_hash": "<string>",
  "line_tax_data": {
    "subtotal": [
      123
    ],
    "total": [
      123
    ]
  },
  "line_subtotal": 123,
  "line_subtotal_tax": 123,
  "line_total": 123,
  "line_tax": 123,
  "product_name": "<string>",
  "product_title": "<string>",
  "product_price": "<string>",
  "product_image": "<string>"
}