You need to update the post parent of the image to attach it to the post, you could to that in the same function that you’re using to set the featured image.
<?php
function acf_set_featured_image($value, $post_id, $field ){
if ($value != '') {
//Add the value which is the image ID to the _thumbnail_id meta data for the current post
add_post_meta($post_id, '_thumbnail_id', $value);
// attach image to post
wp_update_post(
array(
'ID' => $value,
'post_parent' => $post_id
)
);
} else {
delete_post_meta($post_id,'_thumbnail_id', $value);
}
return $value;
}
// acf/update_value/name={$field_name} - filter for a specific field based on it's name
add_filter('acf/update_value/name=cursusfoto', 'acf_set_featured_image', 10, 3);
?>
