Shankara says that this world is not true which is like a dream. But Ramanuja says that even the dream is true. How do you correlate these two?] Shankara never said that this world is not a truth. He said that this world is Mithya. Mithya means very little truth, which can be almost considered as untrue. The dream is Mithya. A person in the dream cannot call it as a dream because he becomes the part and parcel of the dream. The ant cannot be Mithya for another ant. The ant is Mithya only for an elephant. Therefore this world is Mithya for the Lord. It is a daydream of the Lord.
There is no ignorance in the daydream and therefore the Lord did not become ignorant. Shankara entered the house of Mandana Mishra even though the doors were locked. Therefore the world was Mithya for Him. Mithya is not untrue. Ramanuja said that this world is not a dream for a soul. The soul is a part and parcel of the world. Mithya is not Mithya for a Mithya. This is the interpretation of Ramanuja. In fact Shankara came as Ramanuja and clarified the misunderstanding.
Sri Datta Jnana Prachara Parishat