Just did this, 5 minutes effort, though that included a minute of brown trousers when it wasn't playing. Couple of notes that would've helped me and may be of use to readers.
Do it in front of a surface you can see reflection of the indicators' flash, as the dash indicators didn't light up.
The initial 6 turns from LOCK to ON had to be done quickly, first attempt (although within 10 seconds) it didn't play, second attempt I really sped it up and it went into registration mode fine.
When doing the 6 turns, make sure you push right through to ON and not one click too short.
I couldn't just register my one problem key, I had to do both.
This manifest itself in the "problem" key starting to work fine but then the "working" key stopping working. So once you get into registration mode, make sure you register both/all keys, even if one of them was already working fine.
After the first key was successfully registered (upon release of UNLOCK) I did not notice an indicator flash, as suggested in the process. I carried on regardless, took the first key out and inserted the second key for registration.
Don't forget to turn the key to ON after you have registered the last key, to go out of registration mode
I simply cannot believe Nissan have the audacity to demand something like £45 for this process which took a monkey (me) 3 attempts and 5 minutes to action correctly.
Usual disclaimers apply, for info only, if you brick your Zed or your key or both, it's not my fault.