You cannot simply download the app on a new phone and log in. Because the "secret seed" is tied to the specific device installation, you must remove the key before you lose access to the old device.
Why it happens: Time drift. TOTP relies on the exact time on your phone. If your phone's clock is off by even 30 seconds, the code fails. The Fix: swtor security key app work
While Google Authenticator works, if you lose your phone, you lose your codes. Authy allows encrypted cloud backups. Install Authy on your phone AND your PC. If one device dies, the other still has the SWTOR key. You cannot simply download the app on a new phone and log in
Most user errors occur because they use the wrong app. The original "SWTOR Security Key App" was discontinued years ago. It no longer works on modern iOS or Android versions. TOTP relies on the exact time on your phone
If you try to download the old "Star Wars: The Old Republic Security Key" app from a legacy APK site, it will NOT work. The certificates are expired.
Even if the setup is a hassle, adding a Security Key to your SWTOR account is 100% worth it because of the rewards: