Hard to define the Title of this Question....
I want to create a nice readable permalink structure for my 2 custom post types (CPT). My first CPT "family" has the following rewrite-slug "family/%postname%" (all works fine)
The second CPT "childs" has a metabox where I can select the parent_id-field by choosing a CPT "family" where the child-CPT belongs to. That also works great.
Now I set the rewrite-slug for "childs" to "%parent_post_url%/child/%postname%" so that I can get the following URL "family/the-griffons/child/peter" . But when I call this URL wordpress displays a not-found-page. The crazy thing is that if I set the rewrite-slug hard to "family/the-griffons/child/%postname%" I can call the URL (both URLs are the same!!!)
So why toes WP throws an error when I try to get the URL dynamically but not when I hardcode the URL??