There are few steps needed in order to set up cards tokenisation and authentication callbacks:

1. Always add an external ID during tokenisation / authentication process via Xendit.js
2. Merchant needs to set up the callback URL first. You can set up the callback URL from this link or Settings > Developers > Callbacks > Cards section
   
   You should click Test and Save button once you have added the callback URL. 
3. For authentication callback, merchant will only receive the callback when the status is VERIFIED / FAILED. If it is still PENDING, there will be no callback sent to merchants. 

How to monitor cards tokenisation and authentication callbacks? 

You can clink on this link or go to the Callbacks tab

Not only monitoring, merchant will also have the option to resend the callback whenever they want to.