What are possible bid_unit values for APP_INSTALLS campaign objective?

[chris_august7]

On the following two pages, I see it mentioned that an app installs campaign can have more than one type of bid unit. What are the possible options?

https://dev.twitter.com/ads/reference/post/accounts/%3Aaccount_id/line_items
https://dev.twitter.com/ads/basics/enums

It seems like its a subset of the enum values for bid unit. Which subset?

bid_unit
APP_CLICK
APP_INSTALL
ENGAGEMENT
FOLLOW
LEAD
LINK_CLICK
VIEW
VIEW_3S_100PCT

[msbukkuri]

APP_CLICK
APP_INSTALL

Just some more detail and my 2 cents:

Take a look at this in the Twitter Ads UI for an App Installs or Engagements campaign:

In the above screenshot, you can see how you can optimize for app clicks or installs, and pay for app clicks or pay for installs.

In the Ads API, the way it works is:
BID_UNIT is optimize
CHARGE_BY is pay for

Hope that clears up the confusion around this.