The type of optimization goal

[Proto definition ![GitHub](https://developers.google.com/site-assets/logo-github.svg)](https://github.com/googleapis/googleapis/blob/master/google/ads/googleads/v25/enums/optimization_goal_type.proto)

| Enums ||
|---|---|
| ## `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. |
| ## `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. |
| ## `UNKNOWN` | Used as a return value only. Represents value unknown in this version. |
| ## `UNSPECIFIED` | Not specified. |