Grisu
Part of the Furniture
I could register your serial, is known as wireless RT-AC86U. Canceled process after it has been validated as correct.There appears to be a problem with the ASUS's web site and compatibility with certain browsers/computers . I went to try and register the new AC86 that ASUS sent me under RMA and after trying all various combinations of K4IAHN000041 it kept being rejected as not valis. Since I have ASUS on my speed dial I called them and they verified that the serial number was valid. They then had me switch from using Firefox to Chrome and their web site still rejected the number.
It doesn't help that the type face they use doesn't clearly distinguish between 1 and I.
I tried on german site www.asus.de maybe this makes the difference.