no api key set error when retrieving stripe customer

public function chargeCustomer () 
{ 
    $plan = Input::get('plan'); $token = Input::get('stripeToken');
    if($plan == 'ito_monthly')
    {
        Auth::user()->subscription($plan)->create($token);
        return redirect('/dashboard');
    }
    elseif($plan == 'ito_yearly')
    {
        Auth::user()->subscription($plan)->create($token);
        return redirect('/dashboard');
    }
    elseif($plan == 'pay-per-item')
    {
        return "to be impleamented later";
    } 
}
public function updateCard()
{
   $cu =  \Stripe\Customer::retrieve("cus_7evdSA5ccyyGc2"); 
}

User::setStripeKey(\Config::get('services.stripe.secret')) this is set in appserviceprovider under boot().

my first function works fine, but for updating card i get api key not set error

via Chebli Mohamed