Google has recently launched pay-for-conversions bidding for the purpose of display ads. This feature will allow advertisers to pay for conversions rather than clicks or impressions. Read more at warc.com
The new feature is aimed at display campaigns. In this process, advertisers have to set a Target CPA in the bidding section of campaign settings. Advertisers will only be charged when users convert on their site. The option will only be available for those using Target CPA with display campaigns.
The algorithm used here is the same as paying for clicks. Advertisers can use this service only when in Google account they have at-least 100 conversions in the last 30 days. Also the time between a click and conversion must be within 7 days for almost 90% of the conversions.
The 'Pay for conversion' cannot be linked to offline conversions for example store visits.