There is a specific symptom that tells you an attribution setup has failed: when you add up the conversions claimed by each channel, the total is meaningfully higher than the number of conversions your CRM recorded. That gap is not a rounding error. It is budget being allocated on fiction.
The causes are usually mundane. A site migration dropped a tag. Consent mode was implemented in a way that stopped events firing for a large share of EU traffic. A form was changed and the event never re-tested. Nobody noticed because the dashboard still had numbers on it.
Start by reconciling three sources: your analytics platform, your ad platforms, and your CRM or order system. Pick the one closest to revenue as the source of truth, then work backwards to find where the others diverge.
Server-side tracking closes most of the gap. Sending conversion events from your server rather than the browser makes measurement resilient to ad blockers, ITP and consent restrictions, and it gives you a single place to enforce consent handling correctly.
The fix is rarely glamorous and almost always worth it. A client who restores trustworthy attribution typically reallocates a meaningful share of budget within one quarter — usually away from the channels that were claiming the most credit.
Do the plumbing before you optimize the campaigns. Optimizing against bad data is how you spend more to earn less with great confidence.