Why is the database search not working?

Question

WordPress

hello i have a code

$wpdb->get_results( "SELECT post_id from $wpdb->postmeta WHERE meta_key = '$results_id' AND meta_value = '".$add_id_iico2."'", ARRAY_A )

A unique product id is inserted into $add_id_iico2. Next, this id is used to search for another id from the wp database.
I used to get id $results_id[0]['post_id'] , but now it doesn't work for some reason.