Did you save those ten backup codes? If yes, enter one when prompted for the six-digit code.
If you aren't receiving it, you can request a by texting "otp" to 32665 from your linked mobile number. Recovery Codes : facebook six digit code
But what exactly is this number? Why does it show up even when you haven’t requested it? And most importantly—should you ever share it with anyone? Did you save those ten backup codes