As of last month, Google has announced that you can now choose to pay for conversions, rather than clicks, when using Display campaigns. Paying for conversions means you only pay when someone converts on your website or app – and you’ll never pay above your target cost per action (CPA). Let’s say your target CPA is £10, and you drove 30 conversions over the weekend. You’ll pay exactly £300, with an actual CPA of £10. You won’t be charged for clicks or impressions. The option to pay for conversions is only available when you use Target CPA with Display campaigns.
Source: Brent Besson, Product Manager, Google Ads