Forum OpenACS Q&A: Re: where can i change the default url for oacs-9.5?
Basically, the url is determined by SystemURL and the info provided in the nsd config.tcl file.
SystemURL needs the "http://" prefix as shown above. The domain in config.tcl doesn't.
ps. As a noobie over the years, I've broken the system a few times by changing that value, where once it was changed I couldn't login to admin to change it back via a browser. I had to access the db via psql. If this is the problem, you can always change it back via the db.