Keep dificulty in hard

Hi, how can i do to keep the dificulty of my minecraft server in hard,
Because yesterday was in hard and this morning the dificulty is in pacific and this breaks my iron farm


If you’re playing in 1.13+, only set your difficulty with the command /difficulty directly in-game.

(By the way, don’t pay attention to the difficulty setting on your admin panel which is stuck at ‘None’ no matter what difficulty you’re currently playing with. It’s a known bug when you’re playing on a 1.13 server or higher, it will be solved as soon as possible)