in_category() self defined $post->ID - wordpress

Question

I have this code:
function add_cert_id_to_notes( $order_id ) {
$order = new WC_Order( $order_id );
$products = $order->get_items();
foreach( $products as $product ){
$product_id = $product['product_id'];
$order->add_order_note( 'First Test: '.$product_id, 0 );
if( in_category('188', $product_id)){
$order->add_order_note( 'Second Test: '.$product_id, 0 );
}
else {
$order->add_order_note( 'Second Test: FAIL', 0 );
}
}
}
Using WooCommerce, but that's not the problem. The issue is with in_category(). I'm not doing this is a standard loop, I've defined my post ID with $product_id.
Problem is, it keeps returning the failure notice I have set up. I've tried with both the category ID and slug and I still get nothing.

Answer 1

I think in_category is only for post's category.
Document says The given categories are checked against the post's categories' term_ids, names and slugs. So it only check for post i think.
Try following function:-
function add_cert_id_to_notes( $order_id )
{
$order = new WC_Order( $order_id );
$products = $order->get_items();
foreach( $products as $product )
{
$categories = array();
$product_id = $product['product_id'];
$order->add_order_note( 'First Test: '.$product_id, 0 );
$terms = wp_get_post_terms( $product_id, 'product_cat' );
foreach ( $terms as $term )
{
$categories[] = $term->term_id;
$categories[] = $term->slug;
}
//if you want to check category slug than you also can use `slug` as $your_cat_id.
//`$term->slug` is also in $categories array..
$your_cat_id = '188';
if ( in_array( $your_cat_id, $categories ) )
{
$order->add_order_note( 'Second Test: '.$product_id, 0 );
} else {
$order->add_order_note( 'Second Test: FAIL', 0 );
}
}
}
I have tested this function and its working...Hope it will work for you..