If you have charged the guest too much, and a refund is required, a credit can be charged without the credit card details of the guest. Log in to https://me.sumup.com/login with your access data.
Click on "Payments" in the left menu to see all transactions. Select the appropriate transaction you wish to credit and click on the "Refund" button on the right. Now enter the partial or total amount to be credited and confirm the transaction by entering the password again. For further instruction, please view.
The credit will be made on the deposited credit card of the guest. A credit will take about 2-3 days (4 days if there is a weekend in between). If you have not received any payment after 5 days, please contact our support by phone on +49 30 20 8989 411 or by e-mail to firstname.lastname@example.org.
For more detailed information, please view here.