This object reports the specific failure code from the most recent feature-key operation, distinguishing causes like a failed file transfer, a serial-number mismatch, a signature verification failure, or a primary/secondary digest mismatch. Admins check this after featureKeysLastOperationState shows setFailure to diagnose exactly why the key or certificate update was rejected. For example, a value of verifySign(4) tells the admin the uploaded signature failed cryptographic verification, likely because the wrong certificate was used.