Then you should complain to the router vendor. Dynamic UPDATE and TSIG were
standardised over a decade ago to allow everyone to use the same protocol.
You should just be able to type in the update server's name if it isn't one of
the zone's nameservers. If it is then it shouldn't be needed.
key keyname <secret>
update delete hostname A
update add hostname 300 A 188.8.131.52