Cost cap

With a cost cap (Meta's interface now labels it "cost per result goal") you tell the platform the average price you can afford for each result. It then bids higher on people it thinks are likely to convert and lower on the rest, aiming for that average. Meta is clear that the cap is a goal, not a guarantee, and that the budget may not be fully spent. A bid cap is the stricter cousin: a ceiling on each individual auction.

Arbitrageurs like cost caps because the business is a spread. If a tracked conversion (for example a search or an ad click on the lander) is worth a known amount, the cap can be set just beneath it so the campaign only spends when the maths works.

The trade-off is volume. Set the cap too low and delivery dries up; set it too high and it stops protecting anything. Caps also depend entirely on the conversion events the platform receives, so delayed or missing postbacks make a capped campaign stall.

An example

Say each feed ad click earns about $0.60 after the provider's share. A cost cap of $0.45 per ad-click conversion leaves a $0.15 cushion per result for clawbacks and fees. If the platform can only find such clicks at $0.50, spending slows instead of losing money.