public function approve($invitationKey)
{
$invitation = Invitation::with('invoice.invoice_items', 'invoice.invitations')->where('invitation_key', '=', $invitationKey)->firstOrFail();
$invoice = $invitation->invoice;
$invitationKey = $this->invoiceService->approveQuote($invoice, $invitation);
Session::flash('message', trans('texts.quote_is_approved'));
return Redirect::to("view/{$invitationKey}");
}