curl --request POST \
  --url https://production.trackstarhq.com/link/token \
  --header 'Content-Type: application/json' \
  --header 'x-trackstar-api-key: <x-trackstar-api-key>' \
  --data '
{
  "connection_id": "existing_connection_id",
  "customer_id": "customer_id"
}
'

import requests

url = "https://production.trackstarhq.com/link/token"

payload = {
    "connection_id": "existing_connection_id",
    "customer_id": "customer_id"
}
headers = {
    "x-trackstar-api-key": "<x-trackstar-api-key>",
    "Content-Type": "application/json"
}

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

print(response.text)

const options = {
  method: 'POST',
  headers: {
    'x-trackstar-api-key': '<x-trackstar-api-key>',
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({connection_id: 'existing_connection_id', customer_id: 'customer_id'})
};

fetch('https://production.trackstarhq.com/link/token', 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://production.trackstarhq.com/link/token",
  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([
    'connection_id' => 'existing_connection_id',
    'customer_id' => 'customer_id'
  ]),
  CURLOPT_HTTPHEADER => [
    "Content-Type: application/json",
    "x-trackstar-api-key: <x-trackstar-api-key>"
  ],
]);

$response = curl_exec($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://production.trackstarhq.com/link/token"

	payload := strings.NewReader("{\n  \"connection_id\": \"existing_connection_id\",\n  \"customer_id\": \"customer_id\"\n}")

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

	req.Header.Add("x-trackstar-api-key", "<x-trackstar-api-key>")
	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://production.trackstarhq.com/link/token")
  .header("x-trackstar-api-key", "<x-trackstar-api-key>")
  .header("Content-Type", "application/json")
  .body("{\n  \"connection_id\": \"existing_connection_id\",\n  \"customer_id\": \"customer_id\"\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://production.trackstarhq.com/link/token")

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

request = Net::HTTP::Post.new(url)
request["x-trackstar-api-key"] = '<x-trackstar-api-key>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"connection_id\": \"existing_connection_id\",\n  \"customer_id\": \"customer_id\"\n}"

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

{
  "link_token": "your_link_token"
}

{
  "error": "<string>",
  "detail": {
    "<location>": {
      "<field_name>": [
        "<string>"
      ]
    }
  }
}