The Android version of Hue Essentials can control the Trådfri gateway. If you get an error, please share it so I can look into it. A screenshot would be helpful.
The iOS version of Hue Essentials does not support the Trådfri gateway. We do not mention anywhere that the Trådfri gateway is supported on iOS. If you are using iOS, please let me know where you saw that the Trådfri gateway is supported.
For a refund, please see the following: All about orders and refunds
Let me know if you have any questions.