Connecting Google cast (Onn or Roku) streaming devices to Xfinitywifi

I purchased a wifi now pass (30 days for $10) and I'm having issues connecting my streaming device (Onn full HD streaming device) to the wifi. When I select the network, Xfinitywifi, it doesn't prompt me to enter in a username or password. I did some research and I believe it has to do with the 2.4ghz and 5 GHz frequency settings. Please help...