Vendor TX Code Error

We have recently had a number of transactions fail due to an invalid Vendor TX Code. This is showing as error 4029 in sage pay.

Can anyone explain what could be causing this? Thanks Sarah

To determine messages from Sage based on their coded numbers errors you can find a thorough list here:

I believe this list is for their simulator but most of the codes are the same on the live side as well.

In this case it is stating that the vendor code the request began with is not the same as what it ended with and that led to a denial of the transmission.

It will be best explained by Sage, however, so I would attempt to contact them on it.