Allow CORS so page-scroll detected

Hi there! I’m trying to build another website (site B) that will show a page from webflow in a popup. The webflow page needs to be scrolled down to the end of page, to trigger the button on Site B to be active.

Currently my tech team ables to get the webflow page to show on the popup of Site B. But it won’t detect that the page have scrolled to the end so the button (on site B) doesn’t activate. Can anyone help me on this? And should I put any custom code to allows CORS (since based on the tech team I need to set true for Allow CORS on webflow). Thank you.

Regards,
Nadya Atmadja