I think you may get that message if Google Nest does not detect a Google Nest camera in the Google Nest "home" where your Nest Aware subscription is active. You can see the "home" where your Nest Aware subscription is active if you go to this link: https://store.google.com/subscriptions?hl=en-US, and select your Nest Aware subscription; the next page displays the name of your Google Nest "home" below the word "Subscriptions". This "home" should be the same home where your camera is installed in the Google Home app.
I'm dropping by to ensure that everything is covered here. I hope that sheds some light on the issue. If you have other questions and concerns, feel free to let me know.
Thanks for your help here, MplsCustomer.
The Subscription Management page for Nest Aware does NOT show an address.
If you click on your current subscription, the next page shows the NAME you have given to your Google Nest "home/structure". The name of that "home/structure" should be the same "home/structure" where your camera is installed in the Google Home app.
You said in your original post that you received a message saying you need to register a comparable device. That's the message you get if you have no cameras or doorbells in your Google Nest "home/structure". So, I am guessing that you may have created more than one "home/structure" in the Google Home app, and your subscription is assigned to one home and your camera is assigned to another.
If you have more than one "home/structure", if you tap on the name of the current home in the Google Home app, you will get a drop-down showing your homes. (https://support.google.com/googlenest/answer/9155535?hl=en#zippy=%2Cswitch-between-homes)
If your subscription is in one home and your camera is in another, you can remove your camera from its current home and add it to the other home. Or you can use the "Contact us" option under "Nest Aware Premier Care" on the page below to "Get 24/7 access to Nest Aware Experts on the Nest Customer Care team. They’re available to answer questions, help you access features, and manage your subscription."
Just one quick final check in here since activity has slowed down. We'll be locking the thread in the next 24 hours, but if you still need help, I would be happy to keep it open. If there's more we can do, just let me know.