A reason why your Xero orders can appear as "Not Ready" in Shiptheory can be due to an option in the Xero advanced settings in Shiptheory. To reach these settings, you will first need to access the Xero advanced settings in Shiptheory. First, scroll to the bottom of your Xero settings and click "Advanced Settings in the bottom left:

From there, scroll to the very bottom of the page and you'll see the settings for "Invoice Statuses":

In these settings, you can select the statuses that you want Shiptheory to put through your orders at, these all being blank will mean that all of your orders will be set to "Not Ready", you can select as many or as few statuses as you want, orders on a status that is not selected in the options will appear like this: 

If you have any questions or issues regarding this, please don't hesitate to contact support.