setCouponCode not working in magento 2?

Question

SalesQuoteCollectTotalsBefore

This observer will dispatch when the shipment is selected. After that, I need to apply a coupon code.

public function execute(\Magento\Framework\Event\Observer $observer)
{    

    $objectManager = \Magento\Framework\App\ObjectManager::getInstance();
    $cart = $objectManager->get('\Magento\Checkout\Model\Cart');

    $couponCode = "FIRSTORDER";
    $quote = $cart->getQuote()->setCouponCode($couponCode)
                              ->collectTotals()
                              ->save(); 
}

I created a coupon code FIRSTORDER. But I try to execute the function I am getting the following error.

"SyntaxError: JSON.parse: unexpected end of data at line 1 column 1 of the JSON data"

How to solve this issue?. How can I apply the coupon code? please share your valuable feedback

Answer 1

Try following way:

namespace SR\Stackexchange\Observer;

use Magento\Framework\Event\Observer as EventObserver;
use Magento\Framework\Event\ObserverInterface;

class SalesQuoteCollectTotalsBefore implements ObserverInterface
{
    public function execute(EventObserver $observer)
    {
        $quote = $observer->getEvent()->getQuote();
        $couponCode = "FIRSTORDER";
        $quote->setCouponCode($couponCode)
            ->save();

        return $this;
    }
}

Tested with M2.2 working fine.