Proof of Payment is a required component of most reimbursement-based grants.   You must show (via data and documentation) that you paid for the item before you can ask for reimbursement for the item.  Canceled Checks, ACH documentation, or credit card receipts/statements may be entered into the proof of payment module.   All proof of payment items may be entered, regardless of whether they are grant-related or not as only those that are associated with an invoice/grant will be shown on grant documents.   This speeds compliance and grant turn in.