TSIG and Apple AirPort Extreme and Mac

I am willing to configure my Apple AirPort Time Capsule router to dynamically update my IP on dynv6. I created a md5 TSIG key and allowed it for all zones, I used the zone as hostname on the router’s configuration, the key name as user and the secret as password… but nothing happens, it does not update.
I don’t see any errors on the router side, Is there a way I debug it from de dynv6 side?
I could test the same feature from my Mac, but maybe someone can point me in the right direction.
Thanks in advance!