What is ROAS, and why does the platform number differ from the accounts?
ROAS (return on ad spend) is revenue divided by ad spend over the same period. The figure every ad platform shows uses revenue the platform attributed to itself, which is not the same as revenue the business actually banked. A 4x platform ROAS and a 4x accounting ROAS are two different claims, and on most accounts only the first one has ever been checked.
The arithmetic is trivial, which is why the metric spread so fast: revenue over spend, expressed as a multiple. The difficulty is entirely in the numerator. Platform-reported revenue is the value of conversions the platform believes it caused, inside its own attribution window, sometimes estimated rather than observed, and usually before refunds, cancellations, failed payments and returns are subtracted. None of those adjustments flow back into the ad account.
The honest way to use it is to measure the gap once rather than argue about it forever. Take a period, take the revenue the platform claims, and take the revenue the ledger recorded for the same period from the same channel. The ratio between them is a real, measurable property of the account, and on accounts with weak tracking or a long consideration cycle it is frequently well below one. Once you know it, platform ROAS becomes usable as a directional signal, because you know what to multiply it by. Until you know it, every ROAS-based decision carries an unknown scaling factor.
Two smaller traps sit underneath. Ad spend in the denominator is media only, so it excludes creative, tooling and management, and a campaign that clears a target on media cost alone may not clear it on fully loaded cost. And a single blended ROAS across products with different margins tells you almost nothing about which product is profitable, because a high-margin line can carry a loss-making one inside the same average for months.