Hello, @willowooddesignsco. I appreciate what you've done so far. Please allow me to provide the details below on why you're unable to connect Squarespace to your commerce channel in QuickBooks Online (QBO).
Currently, Squarespace is unsupported by QuickBooks, which prevents you from connecting it to your commerce channel. As a result, when you select the Squarespace from the dropdown and click Next, you receive the message: "Thanks for your feedback! Your feedback helps us improve this experience for you and customers like you."
At this time, the sales channels supported by QuickBooks include Etsy, Amazon, eBay, and Shopify.
Additionally, you can refer to this article for more details and guidance on connecting sales channels in QBO: Connect a Sales Channel with Commerce in QuickBooks Online.
Furthermore, I've attached this article for reference if you need to disconnect third-party apps in QuickBooks: Disconnect an app and change subscription.
Please let me know if you need further clarification on managing your sales channels using the commerce feature in QuickBooks. I'm always here to help you.