God or Lord? Acts 19

Acts 19:20"So mightily grew the word of God and prevailed.""This verse contains a controversial translation in the KJB. The problem with this verse is the word "God" and the fact that the Greek text does not use the normal word that is translated "God." The normal Greek word for "God" is ????, theos. The word used in Acts 19:20 is ?????? (Kurios), which is normally translated "Lord." The critics tell us that the translation should be "word of the Lord," rather than "word of God." Is this an error in the KJB? Is it a difference between the Textus Receptus and the KJB?Most Greek teachers would say it is a difference and an error. In this book you will learn one more reason why you can fully trust the King James Bible."