Have you enabled Dynamic Linking?
There are a number of critical points to note.<br/><br/>
You may need to attempt authorisation / authentication over many channels and so the Dynamic Linking authentication code used should be different on each channel to prevent collisions / duplication.<br/><br/>
In addition, it is important to understand that you do not need to present the authentication code to the user, it just has to be used to secure the accuracy / validity of the payment details that are presented to the user for authorisation.<br/><br/>
If the name or the amount changes then you will need to invalidate the authorisation request and related code.