Which segment is sent only if the destination had a problem with the message?

The ERR segment is specifically designed to convey error information when there is an issue with a message being processed. When a receiving system encounters a problem, such as a validation error or processing failure, it will send an ERR segment as part of its response to indicate the nature of the issue. This segment helps to clearly communicate the details concerning the error, enabling the sender to understand what went wrong and take appropriate corrective actions.

In contrast, the MSA segment primarily deals with message acknowledgment, confirming receipt and whether the message was processed successfully or not, while the MSH segment contains the message header information that dictates how the message is structured and how it should be processed. The EVN segment typically conveys event-related information and is not used to indicate errors specifically. Thus, when a destination encounters a problem with a message, the ERR segment is the appropriate and designated way to signal that there was an issue.