Muslim Leadership Casus Belli (Pls answer asap)

Hello everyone I started a camapign with Ottomans I expanded well enough and rivaled the Mamluks, got myself the Muslim leadership casus belli and attacked them, in the Casus belli description though at the declaration page it tells me to occupy Cairo and get 80% warscore and wait, I've been waiting and nothing happened pls help, what is exactly that casus belli?