Paying a supplier's charity rather than the supplier

Our clients are actually our suppliers so we pay them for purchasing waste oil. We normally require an invoice from them so that we have an audit trail and pay either by bank transfer or cheque. One client has asked us to pay their charity rather than themselves. Should I still request an invoice from the company, pay them and leave them to pay their charity or is there another easier/quicker way to pay their charity direct? I have noticed that there is a category for “donations” in Quickfile.