My wife and I are being flown out to a congregant’s son’s wedding. The Baal Simcha told me to buy the tickets, and he would reimburse me via Zelle. The tickets came to $1130, which I put on my credit card. He Zelle’d me $1200. I’m assuming he intends for me to keep the difference, which can certainly be justified by incidental expenses I will be incurring on this trip. But is it ribbis, since it is a repayment for more than I laid out? Or is ribbis not even in play here, since I did not lend him any money – I simply incurred a credit card debt at his behest, and he is sending me a gift of money that will, in its course, cover that debt?
When you laid out he money for the ticket which he was supposed to pay for, that was considered a loan to him, and when he paid you back extra, that could potentially be ribbis. the idea of a present, does not help us here, because ribbis applies even if the person who got the loan wants to pay it, and wants to give the lender a present. Nevertheless, we are not allowed to give a present at this point. there are plenty of other times that we may give a present, but not when paying back a cash loan.
However in your instance, we can assume that the sponsor would want you to use the extra money to pay for other expenses that you would incur during your trip, such as gas, transportation expenses. therefore if you will use that money for other expenses for the trip that would be permitted, however if you don’t have more than $70 in side expenses, you would have to reimburse him that sum.