Xfinity Remote Won't Control Toshiba TV Volume, On/Off

Hello. I recently purchased a new Toshiba Fire TV (Model: 50C350NU). I have tried to pair this new TV with my Xfinity voice remote so that I can control all of the TV's functions through the Xfinity remote,, but it will not pair for volume control or on/off. I have input all the codes as suggested by the Xfinity pairing prompt, but it still does not work. Is there a secret fix that I should be looking into? Suggestions, please.