The flags available on FlyOrDie are limited to recognised sovereign countries and territories. Regional, state, political, historical, military, or other special-interest flags are not available for selection.
This approach helps keep the system simple and consistent for everyone, while also avoiding unnecessary disputes regarding politics, regional identities, or other sensitive topics that can easily lead to disagreements within an international community.
So while the Texas flag is certainly well known, only the standard country flags that appear in the selection list can currently be used on FlyOrDie.