Restrict client/Buyer to order from one vendor/author at a time

The title tells what I want to achieve, I do have a small issue

Here is the code I have added to my function.php file

add_filter( 'woocommerce_add_cart_item_data', 'woo_custom_add_to_cart' );

function woo_custom_add_to_cart( $cart_item_data ) {
	global $woocommerce;
	$items = $woocommerce->cart->get_cart(); //getting cart items
	$_product = array();
	foreach($items as $item => $values) {
		$_product[] = $values['data']->post;
	}
	if(isset($_product[0]->ID)){ //getting first item from cart
		$prodId = (int)$_POST[“add-to-cart”];
		$product_in_cart_vendor_id = get_post_field( 'post_author', $_product[0]->ID);
		$product_added_vendor_id = get_post_field( 'post_author', $prodId );
			if( $product_in_cart_vendor_id == $product_added_vendor_id )
			{return $cart_item_data;}
			else
			{wc_add_notice( 'Whoa hold up. You could only add items from one vendor at a time in your cart', 'error' );}
	}
}

But the if else statement is not working, it’s adding the product to the cart and showing an error message too, please help me to resolve this issue. 🙂

https://wordpress.org/plugins/woocommerce/