When using cost–per–acquisition (CPA) bidding, an advertiser bids using a maximum CPA and pays by:
Question is about MAXIMUM CPA, which is a dead feature and was replaced long time ago. We are using Target CPA not maximum CPA now. Really difficult to find a reason why Google keeps this questions actual. As its Max CPA.
Target CPA bidding uses your conversion tracking data to avoid unprofitable clicks and get more conversions at a lower cost. Based on your campaign’s history of conversions, Target CPA bidding automatically finds the optimal cost-per-click (CPC) bid for your ad each time it’s eligible to appear. It sets higher CPC bids for more valuable clicks and lower CPC bids for less valuable clicks.
Read more here: https://support.google.com/adwords/answer/2390684
Target CPA is an automated bid strategy that sets bids to help get as many conversions as possible at the target cost-per-acquisition (CPA) you set. Target CPA is available as either a standard strategy or as a portfolio strategy
Read more here: https://support.google.com/adwords/answer/6268632?hl=en&rd=1