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, First Log in to the Xero developer portal, then click My Apps -> Add Application. Choose the Auth Code application type.
Enter a name for your application and the URL of your company. This information is displayed to users when they connect.Register the Redirect URI appropriate for the product you are using, https://localhost:3333 will work well with on-premise CData products and https://oauth.cdata.com/oauth/ will work with products like Connect Cloud, but any valid redirect URL would work.
After you click Save, you are shown your OAuth Client ID and can create a new OAuth Client Secret. You will set these to OAuthClientId and OAuthClientSecret
After setting up a custom OAuth application, set the Auth scheme to OAuthClient, paste in the OAuthClientID and Client Secret from the application you just created. Finally, set the Callback URL to the value you used for Redirect URI in the Xero portal.
With these values set, the driver should now be fully functional.
More info on this limit can be found at the below page, which is for the ODBC driver but valid for most CData products that interact with the Xero API
https://cdn.cdata.com/help/DXJ/odbc/pg_xeroapilimits.htm
