What is meant by “back activity” is actually when a user press back button on RDP payment page. (The orange circled one in the following picture). This is ONLY applicable for RDP hosted payment page.
Fig 8-1. Back button inside RDP hosted payment page.
This activities means that the Card Holder would like to go back to the Merchant site to re-think about what they want to purchase. RDP is going to directly redirect the Card Holder to the Merchant’s site sent as in back_url field when Merchant do request of the First Phase (see the First Phase Section).
It is recommended for the Merchant to correspondingly prepare the user experience to continue as is the meaning conveyed of this “back” button.