You can use target cost-per-acquisition (CPA) bidding to help:
get as many conversions as possible within your budget
get as many conversions as possible within a flexible budget range
get as many clicks as possible within your budget
generate more clicks than manual bidding would generate
Target CPA is an AdWords Smart Bidding strategy that sets bids to help get as many conversions as possible at the target cost-per-acquisition (CPA) you set. It uses advanced machine learning to automatically optimize bids and offers auction-time bidding capabilities that tailor bids for each and every auction. Target CPA is available as either a standard strategy in a single campaign or as a portfolio strategy across multiple campaigns and ad groups.
If your main advertising goal is getting conversions (like sales, signups, or mobile app downloads), then Target CPA bidding can help automatically get more conversions for your budget. It can also help you get more sales while paying less for the clicks that lead to those purchases.
Read more here: https://support.google.com/Google Ads/answer/2390684?hl=en