The Fortify On Demand URL indicates to the plugin which Fortify On Demand system it should connect to.
The Fortify On Demand URLs are:

https://emea.fortify.com [Africa, Middle East and Europe]
https://apac.fortify.com [Asia and Pacific]
https://ams.fortify.com [Americas]
https://sgp.fortify.com [Singapore]
https://trial.fortify.com [Trials]
https://sandbox.fortify.com [Development]
https://fed.fortifygov.com [US Federal]

Custom deployment URL rules:
Protocol: the system only supports http and https
Port number: any valid port number
DNS: a valid domain name or hostname

Important:This property cannot be blank, end with the character "/", contain spaces, or include DNS restricted characters