Thanks! With my games I do try to go for a harder difficulty curve, since that is the type of game I like most. I should have probably warned you about that, sorry!
As for level 4, the thing you're missing is (rot13) : Jung erpbzovavat gur obggbz ybpx pna qb sbe lbh.
Edit: Just saw that you beat level 4 in the Discord, congrats!