For the previous releases of Codebook for iOS, the dismiss button wasn’t appearing on all devices, but starting in version 5.2.0 the dismiss button should always be present in the upper right hand corner and you can also swipe down to dismiss it. The latest version of Codebook for iOS is 5.2.1. If you haven’t already, please update to the latest version and you should be able to dismiss the prompt the next time it appears.