As the Payments account (powered by WePay) [Name pending] owner, navigate to the payment details.
The direct link to the account login for wepay is https://www.wepay.com/login This user will have been created when you signed up for your wepay account.
The Issue Refund button will not be available to users other than the account Owner.
It will also be unavailable if the payment is over 60 days.