25 C.F.R. § 101.21
Repayments on United States direct loans shall be made to the authorized collection officer of the Bureau of Indian Affairs who shall issue an official receipt for the repayment and deposit the collection into the revolving loan fund. Collections will first be applied to pay interest to date of payment and the balance applied on the principal installment due. Collections on loans made by relending organizations which have been declared in default in which the Commissioner has taken control of the assets of the program (including loans made with balances owing) will be made to an authorized collection officer of the Bureau of Indian Affairs who shall issue a receipt to the payor and deposit the collection in the United States revolving loan fund. The relending organization's loan from the United States will be credited with the amounts collected from its borrowers, with the collections applied first on interest accrued and the balance applied to the principal. Payments on United States direct loans may be made in advance of due dates without penalty.
25 C.F.R. §101.21