I get this error when I am accessing the web app after it has been installed
Error trying to configure Nintex Web App -SharePoint online
+23- Nintex Employee
Download SharePoint Online Management shell, connect to your tenant and run the command and wait about 5 minutes.
Set-SPOTenant -DisableCustomAppAuthentication $false
Set-SPOTenant -DisableCustomAppAuthentication $false
+23- Nintex Employee
I just ran this command on a new tenant at the time of advising you to do so and it worked for me. I doubt Microsoft have depreciated it between then and now. Make sure that the SharePoint Online Management shell is up to date.
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