Hey there @madhattercaps,
Thanks for joining the community! We are so thrilled to have you!
The error you are seeing there is indicating that some part of the information entered for the connection was incorrect and Shopify is blocking this connection.
To fix this issue you will need to ensure that your credentials are correct as well as the URL being used for the connection. Please review these Shopify connection steps entirely and precisely when re-attempting that connection.
I hope this helps! 🙂