@JFerr,

I think the main tell, other than the error message will be the LED Status.

From this FAQ: Main Deco Fails to Setup

Unable to create WiFi network; Error Code: Failed to connect to TP-Link Cloud/Unable to apply your network settings/Failed to create Wi-Fi network.

Check the LED status on the main Deco:

• if the LED is solid green/white, it means the Wi-Fi has been created already. You can force the Deco app to close and go to the Settings -> Wi-Fi page of the phone to manually connect to the new Wi-Fi network.
• If the LED is still pulsing blue, please set it up again with a different Wi-Fi name.

If the LED is Green/White: It sounds as though the app may need to refresh its interface after the setting gets applied; following the instructions above, closing the app, or even restarting your phone

Otherwise, you may consider trying the setup again, resetting the device to defaults, or configuring another node as your main (if configuring multiple)