I just tried to use SoapUI to connect to the https://connect.squareupsandbox.com/v2/payments but got this error message:
Error getting response; java.net.SocketException: Permission denied: connect.
could you help check what happen in sandbox environment?
I took a look at the logs and am seeing call to ListPayments but I don’t see any calls to CreatePayment. What are you passing in for the payment request?