Whilst integrating Opayo (Formerly Sage Pay) using C# with .Net, I was having some issues with getting a payment registered using the "Form Integration" method, this included finding a definitive way to encrypt the "Crypt" field. With the help of the Opayo tech support, who are refreshingly responsive, who supplied an example encoded string, and looking at many code examples, we fixed all the issues. We are using the Opayo Form Integration, using the Version 4.00 protocol,