Hi, I just solve the issue editing wp-gpx-maps/wp-gpx-maps.php file. In the function enqueue_WP_GPX_Maps_scripts() you can find
wp_enqueue_script( ‘googlemaps’, ‘//maps.googleapis.com/maps/api/js?……
just remove the deprecated parameter and add the required one
wp_enqueue_script( ‘googlemaps’, ‘//maps.googleapis.com/maps/api/js?key=[YOUR GOOGLE API KEY]’, null, null);
I apply this solution https://wordpress.org/support/topic/google-maps-api-error-missingkeymaperror-1/ becouse the error I receive was “Google Maps API error: MissingKeyMapError”
Could be a good improvement to add a new setting parameter in order to manage google api
hope this helps