Ok got it, for user field actually one has to add “user_” before the id for it to work. So in my case:
update_field( $cover_custom_field_key, $cover_id, "user_2" );
Ok got it, for user field actually one has to add “user_” before the id for it to work. So in my case:
update_field( $cover_custom_field_key, $cover_id, "user_2" );