5 C.F.R. § 1303.50
(a) Acknowledgments of requests. OMB will assign an individualized tracking number to each request received that will take longer than ten days to process; and acknowledge each request, informing the requester of their tracking number if applicable; and, upon request, make available information about the status of a request to the requester using the assigned tracking number, including—
(c) Adverse determinations of requests. Adverse determinations, or denials of requests, include decisions that the requested record is exempt, in whole or in part; the request does not reasonably describe the records sought; the information requested is not a record subject to the FOIA; the requested record does not exist, cannot be located, or has been destroyed; or the requested record is not readily reproducible in the form or format sought by the requester. Adverse determinations also include denials involving fees or fee waiver matters or denials of requests for expedited processing. In the case of an adverse determination, the FOIA Officer will immediately notify the requester of—
[84 FR 22951, May 21, 2019, as amended at 89 FR 48825, June 10, 2024]