What I can do when see "This device is already registered to another account."

Options

Even after removing the device from the organization, it remains tied to the previous owner's account.

To register the device, download the Nebula Mobile App (Android / iOS) and scan the QR code sticker on the device.

Refer to the following guides for instructions specific to your product line:

Access Point

Switch

Firewall (ATP/USG FLEX)