If your business is exempt from US sales tax, after upgrading to paid service, open a ticket and attach your exemption certificate. After our billing specialists review your information, you'll be notified about your exemption status.
Any changes to your billing information will require another application for exemption.
Note: Your site must be active to apply for tax exemption. We can't apply tax exemptions to trial or expired sites.
According to SquareSpace's article on US sales tax and Squarespace billing, in the Tax exemption certificates section: