Here is the solution .
Go to wp-seo-structured-data-schema/lib/classes/KcSeoHelper.php
Open this file and search for kcSeoPostTypes() function.
you will see something like this.
$post_types = get_post_types(
array(
‘_builtin’ => true
)
);
change it to.
$post_types = get_post_types();
Thanks Phil for such awesome plugin!
