Electrum Server (electrs) installed but not connecting to Bitcoin Core

I also see this error message when I run docker-compose logs electrs: No such service: electrs

I have never seen any movement on the progress meter, stuck at 0%

How can I verify whether electrs is able to talk to bitcoincore?

Edit: after further searching, I think this thread here is exactly the same issue I’m describing. Maybe it’s best I reply over there.