The message comes from a GeoDirectory block or shortcode that needs a field key and does not have one. GD > Post Badge and GD > Dynamic Content show “field key is missing”, and GD > Post Meta shows “key is missing”. When the text appears on every listing, the block without a key is in a template that every listing uses.

1. Go to GeoDirectory > Settings > General > Pages and open the page set as Archive item page. It controls how each listing looks on category pages, search results and GD > Listings, so one broken block there shows on every listing.
2. If the message is on the listing pages themselves, open the Details Page from the same screen.
3. Look for GD > Post Badge, GD > Post Meta or GD > Dynamic Content blocks with an empty Field Key. In shortcode form that looks like [gd_post_badge] with no key.
4. Choose a field for the block, or delete it, then update the page.

A post type can have its own Archive item and Details pages in its settings (for example Places > Settings > General), so if you use several post types, check those pages too.

A correct block names the field, for example [gd_post_meta key="address"]. See GD > Post Badge and GD > Post Meta for their settings.