I had to use my WiFi router and not my WiFi extender to connect my new bulbs and plugs. Also make sure you wait a few seconds when connecting when you have a VPN app. On what you are using to add product. The VPN will ask you if the wifi item is safe.
Your repeater/extender is likely set to another SSID, sometimes the same as your main rounded with a “_EXT” name. If you configure the devices for the repeaters I’d it should work.