add_action( 'woocommerce_add_to_cart_validation', function( $is_allow, $product_id, $quantity ) {
$product = get_post( $product_id );
$product_author = $product->post_author;
//Iterating through each cart item
foreach ( WC()->cart->get_cart() as $cart_item_key => $cart_item ) {
$cart_product_id = $cart_item['product_id'];
$cart_product = get_post( $cart_product_id );
$cart_product_author = $cart_product->post_author;
if( $cart_product_author != $product_author ) {
$is_allow = false;
break;
}
}
if( !$is_allow ){
// We display an error message
wc_clear_notices();
wc_add_notice( __( "You already have products of a different seller in cart. You can only purchase from one seller at a time.", "marketking" ), 'error' );
}
return $is_allow;
}, 50, 3 );