Thanks for your replies and help with this. I've checked the android app and the realm is not set. The windows installation and the same for the mac version contains no option for the realm.
Hi - On the server (PCS VPN gateway device) check the 'Sign-in Policies' to ensure the URL/host you configured does not have the admin realm attached to it and only has the user realm.
Once that is fixed and if it still does not allow you to sign-in the server side logs are the next place I would check for possible clues.
And under sign-in policies there is a setting labelled 'Restrict access to administrators only', make sure that is unchecked. Though if that was the case login from android would fail as well, unless you logged into the admin session on Android.
Thanks for your support so far; the company that supports the server have returned with this article. I'm a touch confused why the mobile app can connect while the desktop app cannot.