The default MTN transfer pin of every new MTN simcard is 0000.
So if you are a new MTN subscriber and dont yet know your MTN transfer pin, use that default transfer pin code (0000) whenever you want to to transfer airtime credit to another mtn number.
Due to the fact that almost every MTN client knows that default MTN transfer pin, it will be very adviceable that you change that default MTN transfer pin to a pin code that is hard to guess to prevent your family members and friends from stealing your airtime credit.
It should be noted that anybody that who knows your MTN Transfer Pin and also has access to your phone can easily steal all the airtime credit in your phone.
How to Change the Default MTN Transfer Pin code.