Hi there,
you'll have to submit a support ticket about this
here, they should be able to tell you the reasons behind the problem.
Based solely on the error message, and having no additional data to corroborate this guess, it sounds to me like your card holder has declined the transaction for some reason.
but to be sure, please take an screenshot of the error message (of the whole page, including the URL bar) and ask the support for their assistance.
-Wraith