What is CPA?
The cost an advertiser pays per converted customer (typically a purchase). Maximum allowable CPA equals (AOV - COGS - shipping - fees) divided by 2. If your current CPA is at or above max-allowable, no creative fix can save the campaign — the unit economics are broken.
CPA is the most important paid-social metric because it determines whether ad spend is profitable. The diagnostic test: take your average order value, subtract cost of goods, shipping, and platform fees, then divide by 2. That number is your maximum allowable CPA. If your AOV is $40 and total cost is $32, your max-allowable CPA is $4 ($40 - $32 = $8, divided by 2). Even a perfect ad cannot hit 2x ROAS at that margin. The fix is product (raise AOV, drop COGS) not creative.
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