Specify the domain name server for reverse DNS lookup.
The filter hook “ip-geo-block-dns” can replace the reverse DNS lookup service on your server if it is slow.
"mu-plugins" (ip-geo-block-mu.php)as Validation timing , you should put your code snippet into
drop-in.phpin Geolocation API folder instead of
functions.php. See My custom functions in “functions.php” doesn’t work. in FAQ for detail.