Refunds API Overview
Square provides the Refunds API to return payment funds to a buyer. A payment to be refunded can originate from a Square product such as Square Point of Sale, Square Terminal, Square Invoice, or any Square payment API such as the Orders API or Payments API. As long as your application has the ID of the payment and the payment is complete, it can be refunded. To learn how to get completed payment IDs, see Retrieve Payments.
If you need more assistance, contact Developer Support or ask for help in the Developer Forums.