Maximum CPA (Breakeven) is the most you can pay per sale or lead without losing money, taking into account product margin, gateway fees, and taxes. When the campaigns' actual CPA goes above this value, the system lowers the budget on its own to stop the loss. It also becomes the main reference for Auto-Scale (instead of generic averages), for evaluating the copies created by Horizontal Scaling, and for promoting New Audience tests. The field is optional but strongly recommended: with it, the AI knows exactly where profit ends and loss begins in your business. It appears as a CPA BE badge on the optimization card.