Guest claiming for compensation for delay in confirmation in payment

A guest made a reservation and asked for a payment link to be sent. It was done as per request. But the issue occurred at the time of the guest's check-out as the balance was still reflecting as unpaid due to latency in updating the amount paid for the reservation. Now the front desk manager seeing the balance as unpaid, asked the guest to pay up. The guest had to wait maybe for half an hour till he chose to make a cash payment therein. We promised the refund for the amount paid online, but guest threatens to file a suit for causing emotional trauma and wants 5 lacs INR as compensation.