Capture Errors in case of paypal payment failed using PayPal buttons

I' using Paypal buttons and payment system is working but i want to capture errors if occur between the payment and save it in database, i'm using laravel framework.

<script>
    paypal.Buttons({
        createSubscription: function(data, actions) {
            return actions.subscription.create({
                'plan_id': "planid"
            });
        },
        onApprove: function(data, actions) {
           window.location.href = "/subscription/";
        },
        onCancel: function(data) {
           window.location.href = "/subscription/cancel"
        },
        onError: function(err) {
           window.location.href = "/subscription/error?error=" + err;
        } 

via Chebli Mohamed