Define maximum number of invoices allowed per user within 24 hours

Add this code to site.php file:

Am_Di::getInstance()->hook->add(Am_Event::VALIDATE_SAVED_FORM, function(Am_Event $e) {
    if (!$user_id = $e->getDi()->auth->getUserId()) return;

    $reg_max = 10;
    $reg_num = $e->getDi()->db->selectCell(
        "SELECT COUNT(*) FROM ?_invoice WHERE user_id=? AND tm_added>?",
        $user_id,
        sqlTime('- 24 hours')
    );
    if ($reg_num > $reg_max) {
        $e->addError(___('Registration from you IP is temporary disabled'));
    }
});