Call to a member function extendTrial() on null

[vaporic]

Hola quiero implementar extendTrial() pero obtengo un error:

$subscription = $order->subscription('monthly')->create($request->conektaTokenId, [
'email' => 'email@example.com',
'name' => 'Nombre'
]);
$subscription->extendTrial(Carbon::now()->addMonth());

Call to a member function extendTrial() on null