It turned out to be quite simple. Just combine the PRO version and the older acf/pre_save_post like this:
1.
In the template, leave out the ‘new_post’ field:
$options = array(
'id' => 'acf-form',
'post_id' => new_post, //if new post
/*Leave this field out of the array!!
'new_post' => array(
'post_title' => 'Test'
),
*/
//...you other options
);
2.
In the acf/pre_save_field in functions/template, create the post here instead:
function my_pre_save_post( $post_id ) {
// Create a new post
$post = array(
'post_status' => 'publish' ,
//Use the ACF fields to create the title or any other field.
'post_title' => $_POST['acf']['field_586e6ada97b7b'] . ' ' . $_POST['acf']['field_586e6ae197b7c']
);
// insert the post
$post_id = wp_insert_post( $post );
// return the new ID
return $post_id;
}
add_filter('acf/pre_save_post' , 'my_pre_save_post', 1, 1 );
As described earlier, only the ACF fields are included in the $_POST.