Get location ID, event start date etc into Gravify forms

I want to get details of the event into Gravity Forms:
What works is the following …

{embed_post:ID} Display the ID of the post/page.
{embed_post:post_title} Display the title of the post/page.
{embed_post:post_author} Display the author ID of the post/page

BUT HERE I GET EMPTY RESULTS … what am I doing wrong?
{embed_post:veranstaltung} Display veranstaltung – this is a custom field defined by me
{embed_post:_event_start_date} Display the _event_start_date /This is from wp_tm-wochenende_postmeta and should be 2022-02-01
{embed_post: _location_id} Display the loaction_id this should be 1

The page I need help with: [log in to see the link]