"Was 100% put into the business."
Then, you should have already deducted it when you spent the money on the business. You deducted it as business expenses or as depreciation of any capital assets you purchased.
You essentially got deductions for spending "other people's money" . You don't get a 2nd deduction when you pay those people back.
Interestingly, if you don't pay that person back, he can deduct the "bad debt". But he has to jump thru some hoops to prove it's a genuine bad debt
