When I setup ADFS I usually browse to the URL in order to test that ADFS is operation https://fqdn.domain.com/adfs/ls/IdpInitiatedSignon.aspx
Although it is not a conclusive test it does give me some level or assurance that ADFS is functioning if this web page responds with the sign in page. However, I setup a new ADFS 4.0 infrastructure on Windows Server 2016 and when I browsed to the URL I received the following error.
"An error occurred. The resource you are trying to access is not available. Contact your administrator for more information."
It turns out the IdpInitiatedSignOnPage property is disabled by default in ADFS 4.0 to enable it use the following PowerShell command on your ADFS servers.
Set-AdfsProperties -EnableIdpInitiatedSignOnPage $True