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/**
 * Redirect the user directly to checkout page after adding a product to the cart,
 * skipping the cart page
 */
add_filter ('add_to_cart_redirect', 'mw_redirect_to_checkout');

function mw_redirect_to_checkout() {
    global $woocommerce;
    $checkout_url = $woocommerce->cart->get_checkout_url();
    return $checkout_url;
}