It is generally possible to find out who used your Discover credit card to make a payment or purchase, including sending money via a cash app or other payment service. To do this, you will need to contact Discover directly and report the unauthorized use of your credit card. Discover will then investigate the issue and determine who made the transaction. To help with the investigation, you should provide them with information about the transaction, such as the date and amount of the purchase and any other relevant details. If Discover can determine who made the unauthorized transaction, they will take appropriate action, including cancelling the transaction and refunding any money taken from your account.