function sa_load_recurring_invoices_addon()
{
    if (class_exists('SI_Invoices_Recurring')) {
        return;
    }
    require_once 'inc/Invoices_Recurring.php';
    SI_Invoices_Recurring::init();
}
function maybe_change_invoice_id($master_invoice_id = 0, $invoice_id = 0)
{
    if (!class_exists('SI_Invoices_Recurring')) {
        return;
    }
    // master invoice
    $master_invoice = SI_Invoice::get_instance($master_invoice_id);
    $master_invoice_id = $master_invoice->get_invoice_id();
    // build id
    $clones = SI_Invoices_Recurring::get_child_clones($master_invoice_id);
    $new_id = $master_invoice_id . '-' . count($clones);
    // new invoice created
    $invoice = SI_Invoice::get_instance($invoice_id);
    $invoice->set_invoice_id($new_id);
}