42 C.F.R. § 110.71
In the event that there is insufficient documentation in the Request Package for the Secretary to make the applicable determinations under this part, the Secretary will so notify the requester, or his or her representative. The requester will be given 60 calendar days from the date of the Secretary's notification to submit the required documentation. If the requester is unable to provide the additional documentation, he or she may provide a written explanation of the reason(s) that the requested documentation is unavailable and the efforts the requester has made to obtain the documents. The Secretary may accept such a statement in place of the required documentation or disapprove the Request for Benefits due to insufficient documentation. If insufficient documentation is submitted in response to the Secretary's letter, the Secretary may disapprove the Request for Benefits.
42 C.F.R. § 110.71