AC785 Web UI not working

 

I’m from the UK and have an unlocked Netgear Aircard 785, as listed here:

 

 

I've used my AC785 a number of times in different countries, but today I've arrived in the USA (New York) and have bought an AT&T data SIM. For some reason, the device is telling me I need to check the APN settings, which doesn't usually happen. However, I've tried to follow the instructions to do this from Netgear's website, as shown here:

 

 

Unfortunately, I cannot login to the device in my web browser. I have used both Safari and Chrome, and neither will allow me to access the device - instead they just tell me that they've failed to load the page.