My integration broke new year 2018 where all transactions failed but returned a partial code (201). The data I am sending has not changed, so I guess something has changed on the Sagepay side. It gets the merchant key and card identifier without any issues.
[edit] The config of the integration is correct, eg vendor name etc, which means we can serve up the transaction details. At some point late 2017 something changed that meant all of our transactions failed (ie, the money didn't go through) but the reponse we receive is a 201 which I think is a partial success(..?). Considering nothing has changed within our code base considering what is being sent to Sagepay, I'm wondering if there has been some change to how the data is used/what needs to be sent.
[edit] Have discovered the sandbox testing stuff. Am still getting the 201, and no more.