The error message occurs when you do not have a Google account connected to your device. To assign the device to your premium account the device needs a unique identifier. This exists only if you have assigned an e-mail address to your device that is also used for purchases in the Play Store. In most cases this is a Gmail address. Please check under device settings / accounts if there is a Google account assigned.
If you are using an Android 6 device, please make sure you enabled the permission to read your contacts. You can check it under device settings / apps / WeatherPro / permissions.