Error when trying to authenticate with OAuth 2.0 App

The Xero website requires that your web browser support at least TLS 1.1 or later and the version of Internet Explorer (used by the FileMaker Web Viewer) either doesn’t support this or does not have this enabled by default. This site provides details of how to enable TLS 1.1/1.2 in Internet Explorer. After enabling TLS 1.1 or later you should be able to authenticate successfully in the fmAccounting Link (Xero Edition) solution.