You'll want to look at §1005.11(d). If you determine that no error occurred you must provide a written explanation and allow them to request the documents you used.
The institution's report of the results of its investigation shall include a written explanation of the institution's findings and shall note the consumer's right to request the documents that the institution relied on in making its determination. Upon request, the institution shall promptly provide copies of the documents.
You also have to honor that much money for 5 business days.