Hi @louise77 ,
Welcome to the community!
What is the set up of your equipments at the moment? I googled Nighthawk AX8 and it shows it is classified as a router, if this is the case you have to use our supplied modem/rrouter and connect the Nighthawk to one of the LAN ports.
Here is some thread that you may find helpful, see link below.
Let us know how it will go.
We're glad that your own device worked with the service.
You may also provide the steps or the configuration that you've done in order for it to work as it may use as a reference by future viewers.