Enviando Mensagens de Texto Com API do WhatsApp Gratis com PHP e Guzzle

<?php

$client = new Client();

$headers = [
    'Content-Type' => 'application/json',
    'DeviceToken' => 'SUA_CREDENCIAL',
    'Authorization' => 'Bearer SEU_BEARER'
];

$url = "https://gateway.apibrasil.io/api/v2/whatsapp/sendText";

$body = json_encode([
  "number" => "5531994359434",
  "text" => "Top, APIGRATIS! Que massa.",
  "time_typing" =>  1
]);

$request = new Request('POST', $url, $headers, $body);
$res = $client->sendAsync($request)->wait();

var_dump($res->getBody());