Sabnzbd on Truenas Scale: Hostname verification failed

I have just installed the Sabnzbd app on my truenas scale. I used the default configuration and after trying do access the WebUI I am presented with the error message: Access denied - Hostname verification failed: Redirecting…

I know what it means but not how to solve it. Also I am wondering why this error occurs, because I am expecting the truenas installer to manage such things by itself.