I created a custom keyboard for IOS 8, but when I try to archive it I get the following error:
ITunes Store error. No software with CFBundleIdentifier from "my project prefix". Check if your package ID is correct.
How can I fix this?
Easy fix -
You need to go to iTunes Connect and create an app with the Bundle ID you created and set it up through Xcode or the Dev Center. Once configured, it will work (unless your application has other issues!)