Do I get charged for error response codes?

All 200-series HTTP response codes are charged, including status codes that indicate ZERO_RESULTS or INVALID_REQUEST. Generally speaking, no 400-series response codes incur any charges with a couple of exceptions.

Charged

• OK
• ZERO_RESULTS
• NOT_FOUND
• INVALID_REQUEST (invalid parameter value)

No charge

• OVER_DAILY_LIMIT
• OVER_QUERY_LIMIT
• REQUEST_DENIED
• UNKNOWN_ERROR
• INVALID_REQUEST (invalid parameter, request parsing error)

References