I don't use square so I haven't read the full terms, but I think it's important that B 15 is under 3. Online Store I. eCommerce Terms

So I think these restrictions only apply to websites they designed or host. I think it would be fine to distribute software under the AGPL and use square for the payment. Or run AGPL software on your own ecom site and use them as the payment provider.

Does this sound right? And if so, I guess they wouldn't want to have to redistribute the modified versions of software?