Sometimes, you might want your customers using the WiFi on your Nebula-controlled access-points to be redirected to a webpage before browsing the internet. This can be a redirection to your hotels' or companies' webpage or the sort of. Also, you might want your customers to access this without registration or at least as less borders as possible.
Unfortunately, you cannot use the Promotion URL feature without using the Captive Portal - however, you can set the Captive Portal for something as simple as a click-to-continue - this will make it easier for your customers to access the internet, since they only have to accept terms of service, or just simply acknowledge a Welcome message:
Setting up the Click-To-Continue Portal
AP > Configure > Authentication:
Setting up the Click to continue & Splash Page/Promotional Page:
AP > Configure > Captive Portal: