external5-apne1-prd-elb-bb8209ae955bc4a4.elb.ap-northeast-1.amazonaws.com AXFR zone transfer

Not an apex domain The domain external5-apne1-prd-elb-bb8209ae955bc4a4.elb.ap-northeast-1.amazonaws.com is not the root of its zone.
Instead, try zone transfer on elb.ap-northeast-1.amazonaws.com .