You have Clicker Communicator (SymbolStix) for iPad and have downloaded the extra PCS / Widgit symbol libraries as in-app purchases, so you need corresponding versions of the Core Vocabulary Sets.
Use the links below to download alternative versions of the Core Vocabulary Sets.
Unfortunately, Apple restricts iPads from downloading uncommon file types. Therefore, please use any other device to download the files, and then transfer them to your iPad via email, AirDrop or cloud storage.
Note: If the symbols in these sets display as red crosses, your in-app purchases are not being recognised (probably due to an Apple ID issue). Please contact Support for assistance.