What adventure did Polydectes suggest that Perseus undertake?

Polydectes tricked Perseus into believing that he was furious for not bringing a gift for his wedding so Perseus said that he would give anything he wants. Upon hearing it, he then asked for Medusa's head, a cursed woman guarded with a lot of snakes in her head that whoever stares at them turns into stone. He asks for Medusa's head because he know it was suicidal mission.