The preferred method for providing missing information to perfect a deficient claim for refund involving the Research Credit is to fax the information to the IRS. The correspondence requesting the missing information will provide a fax number for this purpose. Alternatively, the information can also be provided by mail. It is important to include the requested information to perfect the claim for refund and a copy of the letter sent by the IRS.
Sources:
Rev. Proc. 2023-11
§ 41. Credit for increasing research activities
FAA 20214101F
