It is optional for signing in, strongly recommended, and required to withdraw.
To turn it on, open Security from your account menu and choose Enable 2FA. Confirm your password, scan the QR code with your authenticator app or enter the key manually, then enter its 6-digit code within 10 minutes. Turning it on signs out your other sessions.
You then see 10 recovery codes, shown once. Store them offline: each works once and lets you sign in if you lose your phone. To turn 2FA off or replace your recovery codes, you need your password and an authenticator code or a recovery code.
If a code is refused, make sure your phone sets its time automatically and wait for the next code. Never share your codes with anyone, including FALKR support. If you have lost both your authenticator and your recovery codes, contact support.