you need to at least have synergy unlocked which requires the completion of the quest "synergistic pursuits" in the metalworks.

Not sure what lvl you need to get it too. I tried to lvl it to augment gear but I haven't had luck getting skill ups on it using techniques from multiple guides. After about an hr here and hr there, using different techniques from different guides im still lvl 1. So I gave up. All my other crafts went up a lot faster. Synergy was just a silly concept to begin with imo