I lent my credit card to someone this morning. He made a purchase from 45.68 nis and then returned to me 46 nis. He said he didn’t have any Agurot coins (and neither did I). Is it okay to take the 46 and return 30 Agürot at a later time? If not how should I have responded?
It depends on what happened between the two of you. If he gave you the 46 shekel at the time that he used the card, then there was no loan, and taking the extra money isn’t ribbis since there was no loan.
However, if he left and brought you the money after wards then it might be ribbis, depending on what kind of credit card was used. If it was a debit card, where the money is taken from your bank account right away, then it is a loan, however if it is a card that gets paid once a month, and the money has not yet come out of your bank account yet, then it isn’t a loan, as you haven’t laid out any money, and it is also fine. Even if such a case, you can take the 46 shekel, but tell him that you will return the 30 agurot later, or that you will give it to tzedakah in his zechus.