Testing Guide from Worldpay: http://support.worldpay.com/support/kb/bg/testandgolive/tgl0000.html
In Admin Setting: Use Installation ID for the field Merchant ID Field
Testing Guide from Worldpay: http://support.worldpay.com/support/kb/bg/testandgolive/tgl0000.html
In Admin Setting: Use Installation ID for the field Merchant ID Field