The MassOrderAck(35=DK) message is used to acknowledge the receipt of and convey the status of a MassOrder(35=DJ) message.
Additional detail from the official source
The content of the acknowledgement depends on the setting of OrderResponseLevel(2427) in the MassOrder(35=DJ) message. Only the order status is provided and not the immediate executions. Executions for the orders in the MassOrder(35=DJ) are communicated using ExecutionReport(35=8) messages.
Message structure 1350 distinct fields
Source order, including nested components and groups. Group counts precede the repeated entries. “Required here” is relative to the enclosing component or group, not unconditional in the message. A dash means not marked required; conditional requirements remain in the source notes. This is a reference, not a counterparty-specific validator.
Includes nested components and groups. Escape clears the filter.