Here is a sample template you can use to write an acknowledgment letter for borrowing money.
To [Recipient name]
Dear, [Recipient name]
This letter is to acknowledge that the lender [Lender name] has agreed to loan me an amount of [Amount] for a duration of [Number] [Days/Weeks/ Months]. It is agreed by both parties that the amount will be made to the borrower [Borrower name] by [Date].
The lender will not be entitled to any interest once the duration of the contract for the borrowed money has expired. The decided amount will be returned to the lender by the borrower by [Date]. If the amount is not received by the borrower by this time, will have to adhere to the terms dictated in the contract.
[Name of borrower]