How to open pop-up window to place code

I create Code for a product in shop software (ecwid) - this code to be connected with the shopping basket button in Nicepage for product to be transferred to basket.

Problem: Having activated the shopping basket button in Nicepage, ususally a pop-up window opens automatically into which you can load the Code. What do I have to do to get this window?

Thanks in advance

Claus