Not a valid Allowed URL - Barclays EPDQ

I am trying to configure card payment using Barclays EPQD system. I have set the Allowed URL in the EPQD CPI Administration settings to the CS-Cart recommended settings i.e. http://www.mydomain.com/



However, when attempting to process a payment, I receive a 'There has been a problem with your payment. Not a valid Allowed URL.'



I have tried various combinations of URL - all to no effect.



I would be grateful for any assistance with this error.