tg_bot_messenger.php

<?php
define('BOT_TOKEN', 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX');
define('SPECIFIC_USER_ID', 'XXXXXXXXXXXXXXXXXXXXXXX'); //telegram id of the user you want to send messages to
define('ENCRYPTION_KEY', 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'); //encryption key for the bot    
define('API_URL', 'https://api.telegram.org/bot' . BOT_TOKEN . '/');

function sendMessage($chat_id, $text) {
    $url = API_URL . 'sendMessage';
    $data = [
        'chat_id' => $chat_id,
        'text' => $text,
    ];
    $options = [
        'http' => [
            'header'  => "Content-type: application/x-www-form-urlencoded\r\n",
            'method'  => 'POST',
            'content' => http_build_query($data),
        ],
    ];
    $context = stream_context_create($options);
    file_get_contents($url, false, $context);
}

function encrypt($data) {
    $iv = openssl_random_pseudo_bytes(16);
    $encrypted = openssl_encrypt($data, 'AES-256-CBC', ENCRYPTION_KEY, 0, $iv);
    return base64_encode($encrypted . '::' . $iv);
}

function decrypt($data) {
    list($encrypted_data, $iv) = explode('::', base64_decode($data), 2);
    return openssl_decrypt($encrypted_data, 'AES-256-CBC', ENCRYPTION_KEY, 0, $iv);
}

$update = json_decode(file_get_contents('php://input'), true);

if (isset($update['message'])) {
    $message = $update['message'];
    $chat_id = $message['chat']['id'];
    $text = $message['text'];

    if ($chat_id == SPECIFIC_USER_ID) {
        if (preg_match('/Anonymous message \(User: (.+)\):/', $text, $matches)) {
            $encrypted_chat_id = $matches[1];
            $user_chat_id = decrypt($encrypted_chat_id);
            $reply = trim(explode("\n", $text, 2)[1]);
            sendMessage($user_chat_id, "Reply from support:\n$reply");
            sendMessage(SPECIFIC_USER_ID, "Your reply has been sent to the user.");
        }
    }

    if ($chat_id != SPECIFIC_USER_ID) {
        $encrypted_chat_id = encrypt($chat_id);
        $forwarded_message = "Anonymous message (User: $encrypted_chat_id):\n$text";
        sendMessage(SPECIFIC_USER_ID, $forwarded_message);
        sendMessage($chat_id, "Thank you for your message! We have received it anonymously.");
    }
}