That error is quite generic, it's hard to tell is issue.
It will also pop-up when you tried to send lightning payments if there's no opened channel,
'opening' or 'disconnected' channel status, poor connection, etc.

When you click on the lightning logo (beside the seed/connection icon), you'll see something like this:

How many channels and nodes do you see?
In the "Channels" tab, what does it say under "status" of the channel?