Are you able to share a screen grab of what you can see?
Also what happens when you try to load this page directly. Add "/#/0/home-view/onboard/ClaimfromDevice" (without quotation marks) after cloud.cambiumnetworks.com in your address bar.
It looks like you already have a user added as well. If the "Add New" button does not work I would try to disable this feature by clicking "Allow device to be claimed using Cambium ID" and saving. And then reenable the feature to see if that clears the error.
But I think there might be somthing wrong with your cloud account, so you might need to raise a ticket with Cambium to get this resolved.