Android devices may require that any computer connecting by adb, "authorize", via a pop-up dialog on the device.
An authorization "key" is then stored in a .android directory on your PC/Mac in your home directory.
On your device, look for a pop-up dialog similar to the images below:
For Android TV:
For the Fire TV:
Confirm the connection and check "Always Allow..."
If the authorization dialog does not appear, try deleting/renaming the .android/adbkey and
.android/adbkey.pub files in your $HOME directory. This should force your device to reauthorize.