I went through the checklist you sent me:
Square Account
Everything is good, and I’m in good standing, as far as I can tell.
API Credentials
Checked all setting in WooCommerce for this, but I couldn’t find what you specifically mentioned, unless you’re referring to the Sandbox, which has already been configured.
Plugin Version
It is up to date.
System Status Report
https://gist.github.com/leafylistings/c7317fef165977bda85f68ba035453ab