Thanks for the reply. I did try installing the plugin. The suitecrm end is fine, the problem is that NEW private applications can no longer be created at the Xero end. Your current clients may not have experienced any problem yet if they had installed a a private application prior to the migration as OAuth 1.0a is still being supported at the moment for existing applications (although this is ending).
The offical notice:
OAuth1.0a is in the process of being deprecated and new private apps can no longer be created. If you're building a new integration you'll need to use OAuth 2.0"
Although you can create a new app (note - not a private application which can no longer be created), the workflow is completely different and built around OAuth 2.0 credential standards structure e.g. openssl keys are no longer used for verification.
If you try creating a new app in Xero you'll see how the issue arises. Hope this helps.