I was having the same issue, but @youdaman ‘s solution ended up working for me. Here is what I ended up placing within functions.php:
// Advanced Custom Fields, Google Map Setup
function my_acf_google_map_api( $api ){
$api['key'] = 'API KEY GOES HERE';
$api['callback'] = 'Function.prototype';
return $api;
}
add_filter('acf/fields/google_map/api', 'my_acf_google_map_api');
I’m sure that can be simplified, but I was happy to get something to work!