To better safeguard you from potential scams, your Trusted Contact must have both a Singapore-registered mobile number and an email address registered with CPF Board, as they will receive a copy of your transaction notifications whenever important CPF transactions or updates are made in your CPF account. 

You should inform the person you are trying to appoint to update their contact details with CPF Board. If this is not possible, you should consider appointing a different person as your Trusted Contact instead.