Attacking Bandit's Fortress

THis is about the ongoing event Bandits couter-attack Stage II - quest School's out.
I cannot attack tthe Bandit's Fortress in the middle of my lands. The crossed sabres do not become white and clickable. What am I doing wrong?
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if you are on stage 2, then you do not yet use your army
click on the camp and see how many bandits there are, and then make that many sticks and stones in the provision house, then drop them on the camp

Thank You very much!