Full Transaction Lifecycle — Subscriptions

$vault_id = 'SUB-' . $_SESSION['user_id'] . '-' . time();
$post = array(
    'security_key'      => YOUR_PRIVATE_KEY,
    'type'              => 'sale',
    'amount'            => $plan_amount,
    'payment_token'     => $payment_token,
    'customer_vault'    => 'add_customer',
    'customer_vault_id' => $vault_id,
    'recurring'         => 'add_subscription',
    'plan_payments'     => '0',
    'plan_amount'       => $plan_amount,
    'month_frequency'   => '1',
    'day_of_month'      => date('j'),
    'start_date'        => date('Y-m-d', strtotime('+1 month')),
    'email'             => $_SESSION['user_email'],
);
$result = gateway_post($post);
if ($result['response'] == '1') {
    db_insert('subscriptions', [
        'user_id'         => $_SESSION['user_id'],
        'vault_id'        => $vault_id,
        'subscription_id' => $result['subscription_id'],
        'status'          => 'active',
    ]);
    redirect('/account?subscribed=1');
}

Handling Failed Recurring Payments

// In your webhook handler
if ($_POST['response'] == '2' && !empty($_POST['subscription_id'])) {
    $sub = db_find('subscriptions', ['subscription_id' => $_POST['subscription_id']]);
    send_payment_failed_email($sub['user_email']);
    if ($sub['failure_count'] >= 3) cancel_subscription($sub['subscription_id']);
}