I found a link that shows how to register these meta fields before the REST API can see them. Here is the link:
https://developer.ww.wp.xz.cn/rest-api/extending-the-rest-api/modifying-responses/
I found out that the Advance Custom Field (ACF) plugin setup the relationship field, and to update it, I use update_field(‘custom field name’,’related post ID, ‘wp_posts ID’);
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This reply was modified 6 years, 8 months ago by carlfost.
OK. It must be created by the Plugin Custom Design. I thought it was native to WordPress.
This picture shows the difference between when I created the registration record from the admin screen, and when I programatically created it.
Relationship Field
