Promoting a monk to prior

[BlindBlake]

I was wondering what do I need to do to promote monks to prior ? In some other games, I managed to promote them but now the game doesn't allow me to promote them althought they are happy, all their needs fullfiled.
I do have my Great Hall in my monastery to unlock the buffs of the masterpiece, maybe it's what's causing the problem...

Thanks in advance for your help !

EDIT : I waited some time and it seems monks can be promoted to prior once they reach level 6 at their craft. I don't know if it's true, correct me if I'm wrong.

[Zoid]

Yes, only level 6 monks can become a prior.