curl --request POST \
  --url https://api.wabox.me/instances/{instance_id}/token/{token}/newsletters/{id}/follow

const options = {method: 'POST'};

fetch('https://api.wabox.me/instances/{instance_id}/token/{token}/newsletters/{id}/follow', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

import requests

url = "https://api.wabox.me/instances/{instance_id}/token/{token}/newsletters/{id}/follow"

response = requests.post(url)

print(response.text)

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.wabox.me/instances/{instance_id}/token/{token}/newsletters/{id}/follow",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "POST",
]);

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

curl_close($curl);

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

package main

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

func main() {

	url := "https://api.wabox.me/instances/{instance_id}/token/{token}/newsletters/{id}/follow"

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

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

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

	fmt.Println(string(body))

}

{
  "updated": true
}

{
  "error": {
    "code": "instance_not_found",
    "message": "Instance not found or invalid token"
  }
}

{
  "error": {
    "code": "subscription_required",
    "message": "Trial expired or subscription inactive. Subscribe in the dashboard to keep sending."
  }
}

{
  "error": {
    "code": "instance_not_connected",
    "message": "Instance is not connected"
  }
}