3D Secure authorisation is a procedure intended to ensure the security of your online card payments.
To authorise a payment, you will typically need to enter a one-time password known as a 3D Secure code, which is sent via SMS. The code is entered on the 3D Secure page, which should open after you confirm the transfer in Paysend by pressing the 'Confirm & Send' button.
The 3DS authorisation process is managed by your bank. Thus, if you haven't received a 3DS code or the 3DS page didn't open, please contact your bank to investigate the issue.