You can definitely use your subscriptions on more than one device provided the device is signed in to the same Apple Account you used when you subscribed. After you've installed the app, you need to restore your purchase. This link will lead you to an article with instructions for restoring your purchase. Please locate and follow the instructions for your specific app.
If you still don't have access to Premium features after completing these instructions, try rebooting your device (power off, wait a few seconds, power back on).