Currently, the credentials embedded and used by default in the Xero drivers have hit a limit imposed by Xero. The CData team is working with Xero to increase this limit, but as that is a slow process, setting up your own OAuth credentials is an easy way to bypass the issue altogether. 

To set up these credentials, use the below tutorial to set up your own OAuth Desktop Application or Custom Connection Application.
https://cdn.cdata.com/help/DXH/odbc/pg_connectingtoxerocustomappcreate.htm

After setting up a custom OAuth application, the below tutorial goes over setting the needed driver properties to use the new connection.
https://cdn.cdata.com/help/DXH/odbc/pg_connectingtoxerocustomapp.htm

Combining these tutorials will bypass the connection limit error, and allow use of the driver to its full extent.