CPA

Most channels report CPA as a metric but bill on impressions or clicks. Paying per conversion is rarer, because the channel takes on the risk that the ad does not convert. A CPA figure is only as good as the conversion tracking and the attribution window behind it.

Gravity offers true CPA billing: you pay per attributed conversion, but only once the account has $5,000 of lifetime spend or Gravity unlocks it. CPA campaigns use a monthly cap, and serving stops when spend reaches it each calendar month. In Gravity reports, CPA, conversions and ROAS are attributed only at campaign level, not per creative.

ChatGPT ads are never billed per conversion, but report CPA. From 2026-11-09, OpenAI’s Help Center describes a Target CPA bid strategy in Ads Manager; its developer docs still describe the older strategies, so the two sources currently differ.

Work out the most you can pay for a conversion before you set a target, and track CPA by channel rather than blended, since each channel attributes differently. Gravity’s CPA billing suits advertisers who already have spend history; new accounts start on CPM. On ChatGPT, CPA is the result of click or impression billing, so a target guides the bidding without capping the cost per conversion. Through Admux, check GET /channels for the objectives and bidding options each channel supports via Admux, and remember that the disclosed markup applies to media cost, so it raises CPA by the same proportion.