PHP
The following code example illustrates retrieving the Relationship Field value from ACF and passing the value to the Ajax Load More shortcode.

NOTE: Remember to select the Post ID return type when creating your field in ACF – see this screenshot.

 

The following shortcode was used to create the Relationship Field (ACF) example.

[ajax_load_more preloaded="true" preloaded_amount="2" repeater="template_29" post__in="'.$featured_posts.'" posts_per_page="4" orderby="post__in" pause="true" scroll="false" button_label="More Posts" button_loading_label="Loading..."]