wordpress – No permitir que productos gratuitos y de pago se compren juntos en WooCommerce

Puedes usar el woocommerce_add_to_cart gancho opuesto al template_redirect gancho.

Cuando se agrega un producto al carrito, compare el precio actual del producto con el precio del producto en el carrito. Si el precio no coincide, elimine el producto del carrito, esto a través de un bucle para que se aplique a todos los productos en el carrito.

Entonces obtienes:

function action_woocommerce_add_to_cart( $cart_item_key, $product_id, $quantity, $variation_id, $variation, $cart_item_data ) {
    // Get current product
    $current_product = wc_get_product( $product_id );

    // Get current product price
    $current_product_price = $current_product->get_price();

    // Initialize
    $is_free = false;
    $notice = false;

    // When current product price = 0
    if ( $current_product_price == 0 ) {
        // Make true
        $is_free = true;
    }

    // Loop through cart contents
    foreach ( WC()->cart->get_cart_contents() as $item_key => $cart_item ) {
        // Get price
        $product_price = $cart_item['data']->get_price();

        // Product price is NOT equal to 0 and current product is free
        if ( $product_price != 0 && $is_free ) {
            // Remove product from cart
            WC()->cart->remove_cart_item( $item_key );

            // Make true
            $notice = true;
        // Product price is equal to 0 and current product is NOT free
        } elseif ( $product_price == 0 && ! $is_free ) {
            // Remove product from cart
            WC()->cart->remove_cart_item( $item_key );

            // Make true
            $notice = true;
        }
    }

    // Optionaly displaying a notice
    if ( $notice ) {
        wc_add_notice( __( 'Some products have been removed from the cart because free and paid products cannot be bought together', 'woocommerce' ), 'notice' );
    }
}
add_action( 'woocommerce_add_to_cart', 'action_woocommerce_add_to_cart', 10, 6 );