Update shipping cost in checkout 2

Question

I would like to update my shipping cost to zero based on a certain payment method selected in the checkout. My approach is to create a before plugin for this method \Magento\Checkout\Model\TotalsInformationManagement::calculate, which content is :

public function calculate(
    $cartId,
    \Magento\Checkout\Api\Data\TotalsInformationInterface $addressInformation
) {
    /** @var \Magento\Quote\Model\Quote $quote */
    $quote = $this->cartRepository->get($cartId);
    $this->validateQuote($quote);

    if ($quote->getIsVirtual()) {
        $quote->setBillingAddress($addressInformation->getAddress());
    } else {
        $quote->setShippingAddress($addressInformation->getAddress());
        $quote->getShippingAddress()->setCollectShippingRates(true)->setShippingMethod(
            $addressInformation->getShippingCarrierCode() . '_' . $addressInformation->getShippingMethodCode()
        );
    }
    $quote->collectTotals();

    return $this->cartTotalRepository->get($cartId);
}

and this is plugin:

    public function beforeCalculate(
        TotalsInformationManagement $subject,
        $cartId,
        TotalsInformationInterface $addressInformation
    ) {
        ...
        /** @var Magento\Quote\Api\CartRepositoryInterface  $quote */
        $quote = $this->cartRepository->get($cartId);
        $quote->getShippingAddress()
            ->setShippingAmount(0);
        $quote->getShippingAddress()
            ->setBaseShippingAmount(0);
        $this->cartRepository->save($quote);
    }

But this doesn't work or neither is the right approach. Do you have any idea how can I achieve this ?

Thanks

Answer 1

No-code solution: You can create a cart rule which grants free shipping if a certain payment method is used. I just validated this on a vanilla install with sample data:

Conditions section:

Actions section: