(Google Map API) Geocode was not successful for the following reason: REQUEST_DENIED

First of all, the problem was loading the scripts as async, remove it..

try that jsfiddle with your API KEY

(function(){
	let mapElement = 'map';
	let address = 'SPAIN';
	geocoder = new google.maps.Geocoder();
   geocoder.geocode({ 'address': address }, function (results, status) {
    if (status == google.maps.GeocoderStatus.OK) {
      var mapOptions = {
          zoom: 17,
          center: results[0].geometry.location,
          disableDefaultUI: true
      };
      var map = new google.maps.Map(document.getElementById(mapElement), mapOptions);
      var marker = new google.maps.Marker({
          map: map,
          position: results[0].geometry.location
      });
    } else {
    	alert("Geocode was not successful for the following reason: " + status);
    }
  });
})();

#map {
  width: 100%;
  height: 350px;
}

<script src="https://maps.googleapis.com/maps/api/js?key=APIKEY" type="text/javascript"></script>

<div id="map"></div>