For those like me who are late to the party, ACF posted a solution. This worked for me on version 4.4.11 of the free plugin.
Drop this in your functions.php file and replace ‘xxx’ with your API key:
function my_acf_google_map_api( $api ){
$api['key'] = 'xxx';
return $api;
}
add_filter('acf/fields/google_map/api', 'my_acf_google_map_api');
https://www.advancedcustomfields.com/resources/acf-fields-google_map-api/
Sometimes I love people…. this is one of those times. Thanks!