Hi,
If you did configure the Dynamics NAV with Office 365 SSO via the demo Powershell scripts that you find on the product DVD (\WindowsPowerShellScripts), you will end up with a link to the debugger / session page like dynamicsnavwinclient/.../debug.
That does not work and will result in page not found. The workaround would be to create the Azure AD App manually.
The changes you would need to make in the relevant customsettings.config file are the following:
CustomSettings.config:
For Dynamics NAV 2018:
For earlier Dynamics NAV releases:
<add key="AzureActiveDirectoryClientId" value="<<Azure_AD_App_APPLICATION ID>>" />
Reply URL in Azure AD App:
For Dynamics NAV 2018:
https://<<webclienturl>>/
For earlier releases of Dynamics NAV 2017:
https://<<webclienturl>>/WebClient
Tip2: for the Reply URL value, you can also choose to directly add the following url as well (if your client ever wants to use Power BI): https://<<webclienturl>>\OAuthLanding.htm (it will save you some time to do this later on via the Assisted Setup wizard)
Tip3: as a best practice also fill in values for the PublicWebBaseUrl and PublicODataBaseUrl
Hope this does help you further.