Please could you explain the Ontological argument with Kant's counterargument?

Anselm's Ontological argument is a bit different to the other main arguments for God's existence (as well as a bit more complicated), being A Priori, rather than A Posteriori. Here, Anselm tries to prove God's existence (whom he defines as the "greatest conceivable being") through logical necessity, rather than inference from observation. Essentially, he argues that if one is to think of the greatest conceivable being it must exist, since if it didn't exist, an even greater being could be conceived of, ie, one that did exist. Therefore, by definition/logical necessity, God must exist. Immanuel Kant, however, points out what he sees to be a fundamental flaw in Anselm's logic. He argues that "existence is not a predicate". By this, he means that whether or not something exists doesn't add any meaning to the idea. Taking a triangle as an example, we may say that it has three sides, or that the sum of its angles is 180 degrees, but to say that it 'exists' adds no real meaning to the idea. In the case of God, the "greatest conceivable being" could still be theorised as the greatest conceivable being, whether or not it actually exists. 'Existence' cannot be part of its definition.