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When you install your new cam and the trial popup appears, close the app. Do not confirm the trial or accept it.
Open the app again and just verify the cam is in the device list. If you already have an available CamPlus license, you can assign it to the cam.
If you need to buy one, go to the services.wyze.com website and purchase CamPlus. Then go back to the app and assign the cam to that license.