A value sent in the wrong currency.

What the platforms do with a value

Both Meta and Google accept a value and a currency (the fields value and currency) on a conversion. With a value, the platform can weigh conversions by money instead of counting them. Ads Manager can then frame return on spend. Without one, every conversion weighs the same. That is the honest default when you do not know what a visit is worth. The currency is not decoration: the platform converts to the account's currency to bid.

What breaks

A client sets one number on their settings row: what a completed visit is worth to them. It is in the money they do business in. The trap is a sender that reads the value off that row while the currency stays fixed in the code (currency: "USD"). In a scale currency the gap is not a rounding error. A company working in forints sends 1,400,000 per visit, which is about $3,800. Sent as USD it is a number the bidding has never seen, and it will chase that with everything it has.

The rule

• A money field is a pair. Store the currency next to the value on the client's row, and pass both to every sender. A value with no currency to state is a value not to send.
• No value is better than a wrong one. If the client has not set a value, send none. Every visit then weighs the same. The platform optimises on count, as it did before, and that is not wrong.
• Uppercase the code, and validate it is one. The platform fails "usd", "Usd" and "US$" in three separate ways.
• Look at the currency in Events Manager, not just the value. The value looks plausible on the row and absurd on the platform. You only see the mismatch where the currency shows.

What this does not cover

• Exchange-rate timing. The platform converts at its own rate on its own schedule. A client who reports in one currency and bids in another sees small drift. That is not this failure.
• Whether to send a fixed value per visit at all. The alternative is a per-job value, which nobody knows until after the sale. Different question.