The One-Time-Password (OTP) is a temporary password generated by Fido and sent to your phone via SMS. It is used to verify your mobile number. You will receive a different OTP each time you have to log in to your Fido Account.
Your PIN, however, is a 4-digit (security) number that you will set on your Account yourself. You are the only one that will know this PIN. Note that you will need both the OTP and PIN each time you have to log in to your Fido Account.