FormulaCPA = ad spend ÷ number of conversions

Target CPA is the highest ad cost you can pay and still make a profit on a sale. If the actual CPA is below the target, the campaign can be scaled.

In 14ads

If there are no conversions, CPA is not calculated and “—” is shown.
The optimisation loop makes no decision until the minimum spend threshold is met; once enough conversions have accumulated, under the default (Balanced) rules it recommends pausing a variant whose CPA is above 150% of the target. Cautious or Aggressive rules can be chosen per campaign.
A target CPA can be entered per campaign; the loop makes its decision against this target and the campaign page shows the result as “ahead of target / on target / behind target”. An unmeasured value is not compared with the target.

How the engine uses this metric from ad production to publishing is on the how it works page; credits and plans are on the pricing page.