Sumber: https://www.callmebot.com/blog/free-api-whatsapp-messages/

callmebot com whatsapp api.php

<?php
$phone = '6281000000000';
$text = 'Tes kirim pesan';
$apiKey = '0000000';
$url = 'https://api.callmebot.com/whatsapp.php';
$data = array(
    'phone' => $phone,
    'text' => $text,
    'apikey' => $apiKey
);
$options = array(
    CURLOPT_URL => $url . '?' . http_build_query($data),
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_TIMEOUT => 30,
    CURLOPT_SSL_VERIFYPEER => false, // Hati-hati penggunaan ini di lingkungan produksi
);
$ch = curl_init();
curl_setopt_array($ch, $options);
$response = curl_exec($ch);
$err = curl_error($ch);
curl_close($ch);
if ($err) {
    echo "Error: $err";
} else {
    echo "Response: $response";
}