3DS is a type of card verification that some card issuers use in some regions. It is very common in Europe.
If you shop online and when paying you are asked to, for example, enter a code from an SMS, or confirm via your issuer's mobile application, this is an example of 3DS.
If you expect that your payment will require 3DS verification, tick the "Use 3D Browser" checkbox in your billing profile.
When you run your task, if it encounters a 3DS challenge, the status will show "Waiting for 3D Secure". At this point, you should click the "Process 3DS" button
The 3DS challenge will show in the browser. Perform whatever actions are necessary to verify the payment.
When you successfully respond to the challenge, payment will complete.