Outlook plugin will not accept username/password

I am not able to log in to the Outlook app as it will not accept my access credentials. I tried deleting and then re-installing the plugin, but the same 'Invalid username password error displays. I have confirmed the credentials by re-logging in to the Calendar web app.

I took the below from the log file:

[13/08/2018 19:48:48] - Zohobusinessplugin.icon : trayiconloaded

[13/08/2018 19:48:48] - Zohobusinessplugin.icon : first sync 0

[13/08/2018 19:49:01] - Zohobusinessplugin.login : Login - 1.1

[13/08/2018 19:49:08] - Zohobusinessplugin.DBSPACE : Timezones added

[13/08/2018 19:49:08] - Zohobusinessplugin.SREQ : Login - 1.1

[13/08/2018 19:49:09] - get uid Invalid user

[13/08/2018 19:49:12] - Zohobusinessplugin.login : Login - 1.2

[13/08/2018 19:49:12] - Zohobusinessplugin.login : Error while login Object reference not set to an instance of an object.

[13/08/2018 19:49:12] - Zohobusinessplugin.login : Error while login Zoho_Mail_Suite_Sync

[13/08/2018 19:49:12] - Zohobusinessplugin.login : Error while login at ZohoBusinessPlugin.LoginFormNew.SignInBtn_Click_1(Object sender, EventArgs e)