I have found the problem and it maybe something to do with the way we have
it set in the administration of the ANZ account.
I have just stopped the module I use from submitting the variable
vpc_TxSourceSubType with a value of SINGLE
You need to contact ANZ and report:
OPTIONAL TRANSACTION SOURCE SUBTYPE FIELD
The value of this field is defaulted by the eGate Help Desk team during the set up of the eGate Merchant details, so in most cases it is not necessary to use this field. Please let the team know if you include this variable so we can confirm the Merchant ID is configured correctly, otherwise unnecessary errors may be occur during testing.