Sorting by Advanced Custom Field

Hi all, I’m trying to sort all posts by advanced custom field (‘event_date’) but it doesn’t seem to be working. What am I doing wrong?

Here’s my code…
[ajax_load_more container_type="div" post_type="events" scroll="false" transition_container="false" orderby="meta_value" meta_key="event_date" order="DESC" button_label="Load More" button_loading_label="Loading More..."]

Any tips would be appreciated!