I want a button that popus up a form to collect emails TO MY SS MARKETING

Site URL: https://www.intuitivedesign.group/links

Hey all.

I searched and it seems like the ONLY way to do this is with a 50$ license to a third party product which is ridiculous. Square Space has to have this enabled somehow. 

So - how can I put a button on my page that when clicked, pops up a email/name grabber that is linked to my SS Marketing List? 
I see lightbox options to put this to a Spreadsheet which is useless for automations in email, and I see a paid third party, but this seems like it's a basic function of this website builder that does not exist for some reason. How can I do this within the squarespace ecosystem (that I've paid a lot of $$ for already)??

THANKS!