If you see this error message, it likely means there was a connection issue to your store. Please follow these steps
1) Log in with your Sandbox Commerce credentials and proceed to the 'Settings' section
2) Select the 'Store Information' section in the left hand menu
3) You will be redirected to a BigCommerce page that prompts you to login. Select 'Log in to Existing BigCommerce store'.
If you're still experiencing issues, please reach out to your customer success specialist for assistance!