What message key should be used to respond to all Additional Information Request Inquiries?

The use of the message key AR - Additional Reply is appropriate for responding to Additional Information Request Inquiries because this key is specifically designed to indicate that the response pertains to the request for additional information. When an agency or individual has submitted a request for further details, using the AR key ensures clarity and maintains consistency in communication. This key helps streamline the process, allowing all parties involved to understand that the response directly addresses their inquiry for more information.

In contrast, other keys such as AI - Additional Information, while related, do not specifically denote a reply to an existing request, but rather could suggest that new information is being provided without the context of a prior request. REQ - Request Reply implies a reply to a specific request but does not encapsulate the idea that it is providing additional details requested. AN - Acknowledgment Notice is generally used to confirm receipt of information and does not serve the purpose of responding to a request for further information. Thus, the AR key is the most suitable choice for effectively communicating in this context.