I tried Lockpick RCM (loaded it directly via TegraRCM Gui), it complained about sept missing because I wasn't using Atmosphere (SX OS user), then it dumped 77 keys. None of them was the master_key_07. I guess I need Atmosphere for that to work?I have all the keys except master_key_7. This is the key point, that update requires that key.
To obtain it you need to be between FW 7.0-8.01 and use lokcpick RCM instead of normal one or to ask a friend for master_key_07
Lockpick RCM is basically a payload that derives the keys on RCM mode
Anyways I just found master_key_07, pasted it in the keys.txt and it works now. Thanks for your help