ACF only stores the ID of the field for the meta_key/meta_value. CF7 (or the add on your using) is directly accessing the meta value and not going through ACF to get the value.
In order to do this you’ll need to create your own shortcode to add here
[dynamichidden manual_url "CF7_get_post_var key='asp_manual_url'"]
instead of using the [dynamichidden] add on. Or, alternately if this shortcode allows filtering so that you can filter the value used in order to get the file url from the ID. You’ll need to ask the authors of the dynamic text extension if the value can be filtered.
