Bid response uses a currency the request did not allow
The response bids in a currency the request did not list in cur.
What it means
The response declares a bid currency that is not among the currencies the request's cur array allows. When the request lists no cur, USD is the shared assumption.
Why it matters
The exchange either converts at a rate you did not price against, rejects the bid, or (worst) compares your 900 JPY against USD bids numerically. All three end with your bid mispriced or discarded.
How to fix it
Bid in one of the request's allowed currencies, converting on your side before pricing. If you must transact in a currency the exchange never offers, that is an integration conversation, not a field to force.
Example that trips it
// request
{ "cur": ["USD"], "imp": [{ "id": "1", "banner": {} }] }
// response
{ "cur": "EUR", "seatbid": [{ "bid": [{ "impid": "1", "price": 2.5 }] }] }The exchange advertised USD only. A bid in EUR is not a rounding problem, it is a bid the exchange cannot settle. Only visible with both documents side by side.
Check your payload
Paste a bid request or response into the tester to see whether this code fires against it, or gate on the id in CI with the CLI: the id is stable, wording is not.
Back to the full diagnostic code reference.