Why a sale can't be traced back to the ad that caused it

The symptom

A sale happens. The payment record carries no campaign, source or creative information, so there's no way to say which advertisement, or which piece of content, actually produced it. The sale is real. It's just un-creditable.

Where it actually breaks, ranked

• A stored campaign tag overwritten by an empty one on a later, untagged visit, by far the commonest fault. Every returning buyer ends up looking direct.
• Payment links that silently discard unusual characters, anything beyond letters, digits, dashes and underscores.
• Redirects that drop the query string between the advertisement and the landing page.
• A checkout running on a different domain, resetting cookies and the stored campaign with them.
• Case and separator drift, where the same source shows up three different ways across three different reports.

The one most teams miss

Campaign tags written into a checkout session don't automatically reach the payment record. They have to be written onto the payment intent's own metadata, on the same call that creates the session, because session-level metadata doesn't propagate to the payment intent or the charge, and the payment intent is what shows up in dashboard search, exports and reporting. Skipping that one line is the commonest reason a business can't reconcile its platform numbers against its bank.

The fix

Capture the five standard campaign parameters at the edge, before any page renders, so a visitor who leaves within a second hasn't taken the answer with them. Keep two stored copies, first-touch (written once, never overwritten) and last-touch (overwritten only by a visit that itself carries parameters). Write the stored values onto the payment record's own metadata at checkout creation, not just the checkout session. Buy your own product through a live advertisement once before anyone else's money is involved, then search the payment dashboard for the campaign and creative identifiers. If they're there, attribution works. If not, you have a page that decorates links.