Good afternoon and thank you for posting on the Final Fantasy XIV Technical Support Forums.

To clarify, you are trying to assign the TAB key to your Tartarus' scroll wheel, correct? Does this TAB key work work on it's own if you were to use the keyboard? Can you assign any other key to the scroll wheel without issue? Do any other key bindings exhibit this same issue?

It looks like this particular device has a program/driver for it (although it is optional). Do you have this installed: https://www.razer.com/synapse-3?_ga=...376.1544559460

We hope we can be of assistance in helping you enjoy the exciting world of Final Fantasy XIV!