Due to the way that it's designed, you can only use Upscope on websites where the Upscope code has been installed. This usually means that you won't be able to follow the client through the co-browsing session onto any third-party website (for example, Paypal). 

Take a look at this article on iframes to learn more about making them work on Upscope: https://help.upscope.io/en/articles/3456693-how-to-make-iframes-work-on-upscope