Hi ConjurePrint,
I unfortunately did not find a direct way to capture contacts from Square to my Mailchimp list. I did manage a couple of work-arounds.
Workaround #1: I edited all my order-related store emails to include a short note to invite them to sign up with a button at the bottom that will link to a Mailchimp signup form. (This was a pain in the ass, since I had to do each one individually, but at least it's there for all purchase related communication.)
Workaround #2: I added a form to my home and about pages that captures the emails to my Mailchimp account. You'll want a tab open to edit your store and another to access your Mailchimp forms. To do this, in the Weebly edit website screen, chose "add section" and select "embed code". Now from your Mailchimp account, go to Audience -> Signup forms -> and select Embedded Forms. Once you get the preview looking the way you want, copy the code and then paste it into the "embed code" section you added to your store site.
Bonus tip: I'm working on also adding a link to the bottom of the description on each item to invite people to sign up for my email list. Easily done by linking a phrase to a sign up form (as long as you have the sync feature turned off, you'll have access to rich text editing in the description box).
Advanced tip: If you want to do a popup form for email signups that get captured to Mailchimp, you can do this too! You'll need to make sure your Mailchimp account is linked to the site you want the popup to appear on. (I can't remember exactly how I did this in Mailchimp, but I remember it being pretty straightforward on that end and it is in Audience -> Sign up Forms -> Subscriber popup). You'll be given a code to copy and paste into a website header. The place to put it in your Square/Weebly store is not the store editor, but Online -> Website -> Integrations -> at the bottom click on "add new code". In the form that pops up, paste the Mailchimp code in the Custom Code box. Be sure to title it something that makes sense to you (I called mine Mailchimp popup form), have it placed in <head>, and save. To design your popup form in Mailchimp, go to Audience -> Signup forms -> and select Subscriber pop-up. Design your popup the way you want it to look. When you're done designing, click the save/publish button and you should be good. The popup can be toggled on and off from the Mailchimp end - at the top of the edit form screen.
Hope this helps! It's all I've been able to come up with to workaround this ridiculous issue, but I think these solutions, though a bit of work up front, will do the job under the circumstances. Plus, it insures that I'm not illegally signing up people by copying/pasting their info from Square to Mailchimp!
