Log into internet via webpage

I have a GL-AXT1800 router. I’m at a Sandals resort and want to connect my router to their internet. They require you to select their wifi SSID as any other. But, they then open a web browser and present a page requesting my room number and last name. This allows me to connect to the internet. When I try to connect my router, by logging into the router admin screen and selecting the Sandals wifi, I don’t get that page to enter my room and last name. I can’t connect my router to the internet without it.
Any ideas?

connect to your router with some device and try opening this page http://detectportal.firefox.com/canonical.html

(their captive portal should appear)