Errors are returned with HTTP 200 and a JSON body: errorId is non-zero, together with errorCode and errorDescription. Client libraries match on errorId / errorCode.

Code	Meaning
ERROR_KEY_DOES_NOT_EXIST	Invalid or missing clientKey
ERROR_ZERO_BALANCE	Not enough balance to create the task
ERROR_NO_SUCH_CAPCHA_ID	Unknown taskId or the task has expired
ERROR_CAPTCHA_UNSOLVABLE	The captcha could not be solved (funds refunded)
ERROR_TASK_ABSENT	The task object is missing
ERROR_TASK_NOT_SUPPORTED	Task type is not supported

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