Here is the screen shot of the error

Have you checked the payment event logs for further details?

Check if in the Setup Website you have the PROCESS AN ONLINE PAYMENT WITH SALES ORDER CREATION checkbox checked. This could be causing the error

The checkbox is checked but it got me thinking as we are trying in sandbox could that checkbox be causing the issue?

That check does only an authorization and not any real capture of funds. Funds will move when you bill from NetSuite.