Used as a return value only. Represents value unknown in this version.
CALL_CLICKS
Optimize for call clicks. Call click conversions are times people selected 'Call' to contact a store after viewing an ad.
DRIVING_DIRECTIONS
Optimize for driving directions. Driving directions conversions are times people selected 'Get directions' to navigate to a store after viewing an ad.
APP_PRE_REGISTRATION
Optimize for pre-registration. Pre-registration conversions are the number of pre-registration signups to receive a notification when the app is released.