Please make sure that you have finished the installer after downloading the app from the Google Play Store.
To do this, please follow the steps below:
1 - Tap the SwiftKey in the list of apps on the device.
2 - Follow the prompts within the SwiftKey installer by accepting the user agreement, enabling SwiftKey, selecting it as the keyboard and personalizing.
Note: To switch between keyboards, go to a text field and longpress and choose "Input Method" (on Android versions before 4.0) or use the keyboard icon in your notification bar (in Android 4.0 and higher).