3D authentication is a security measure used to authenticate card holders.
3D authentication provides an extra layer of protection for transactions in 'card-not-present' scenarios, and is designed to prevent payment fraud and unauthorised transactions.
If you are having issues with your billing verification, and it is because your 3D authentication has failed the 3D Secure authentication step you will need to contact your bank, and get them to authorise this and future Inkpay transactions.