Quick heads-up for anyone trying this: the 48-hour window starts the moment your account is created, not when you find a working code. If your account is already a couple of days old, check whether Settings still shows the Redeem option — once it's gone you can't add any code later.
If you just signed up, my code is 0052YD (redeem in the app via Settings → Redeem token, or on web via Settings → General → Usage → Redeem invite code). We each get 1B tokens when it goes through; the exact reward is shown on the redemption screen before you confirm. Recently verified it's still working.