Can't pair to my android phone

I finally got and recent android phone with blutooth LE (redmi note 11)

I’m trying to setup the app the it doesn’t seem to work. The app doesn’t display the “scan” button that should be here. I was able to pair my phone with the opz, but it still would not appear in the app.
I restarted everything, and now I can’t even pair my phone with the OPZ: the opz “rejects the connection”. Any idea ?
Thanks !

Update: I was actually able to connect and use it for a while (it’s great !)
But it’s really unstable, the opz just keeps disconnecting for no reason.