Trigger popup from external URL link?

I took over an Elementor (Pro) site recently. There is an existing popup that’s triggered by a button in the page footers. I know how to “harvest” the correct URL to make a link to open the popup. The resultant link code works anywhere on the site. No matter how I specify the URL, it will not open from, say, a link on a different website. The link looks like this: https://staging.mysite.org/elementor-action%3Aaction%3Dpopup%3Aopen%26settings%3DeyJpZCI6IjE5NDAiLCJ0b2dnbGUiOmZhbHNlfQ%3D%3D – which I realized might not be working because it’s a hashed string. It converts to this: https://staging.mysite.org/elementor-action:action=popup:open&settings=eyJpZCI6IjE5NDAiLCJ0b2dnbGUiOmZhbHNlfQ==

The unhashed full URL takes me to the PAGE on the site containing a button that is used to trigger the popup, but it does not present the popup, which is just a sign-up form. I have tried various syntax alterations, but no joy.

In any site page, the URL: “a href=”#elementor-action:action=popup:open&settings=eyJpZCI6IjE5NDAiLCJ0b2dnbGUiOmZhbHNlfQ==”

pops the same popup every time.

Anyone know how to express the URL so that it would work from an external (different) site?