A lot of access points support both frequencies. While it is not possible for Monument to connect to 5GHz networks, it can work perfectly fine when other mobile devices use 5GHz.
Access points usually have different SSID for 2.4GHz and 5GHz. Here's the list of networks shown on an iPhone. As you can see there are two different names for the same router, one for the 2.4GHz and the other for the 5GHz connection.
Initially when setting up Monument switch to the 2.4GHz SSID on your smartphone and complete the setup. After the initial setup you can switch back to using 5GHz.