Additional keys are programmed into a Toyota Yaris from 1999 to 2006 using a manual procedure. To do this you must be in possession of a master key that starts the vehicle.
The key programming procedure is available here:
Toyota Yaris 1999-2006 key programming
Alternatively... if a key that starts the vehicle is brought or sent to us we have the facilities to copy the transponder chip within it onto a new one. The new key will then start the vehicle without any further programming being required. Email us at firstname.lastname@example.org for further information.