‘The Ontological Argument fails because existence is not a predicate.’ How far would you agree with this claim?

St. Anselm acknowledges this in his ‘Proslogian’ that his argument is based on the quote from Psalm 14:1. The Ontological Argument is an A Priori argument of which Anselm seeks to prove and validate God’s existence from definition to reality. Anselm holds the belief that the concept of a being than which no greater can be conceived, he extended his argument, reasoning that if God is the greatest most powerful being by definition, the concept of the existence of God is so sublime to not only exist in our minds but in reality as well. So a being than which no greater can be conceived – i.e. God, the explanation stands, God must exist.However, the argument presented reveals many weaknesses that one could postulate that a reason why the Ontological Argument fails because existence is not a predicate. Particular philosophers that agree are St. Thomas Aquinas, Guanilo and Immanuel Kant, who of which have questioned and or rejected Anselm’s argument completely.