Cannot assign request address (exit 48)

After some manipulation, I’m now getting an error on the Router side: it cannot connect to the Config Server via its IP. This is what I place in a configuration file (just as in the tutorial):
sharding:
configDB: ConfigReplSet/PrivateIPv4:port

The port is defined in the Config server configuration file as well.
This is what I get in my logs:
“errorMessage”: “HostUnreachable: Error connecting to 172.31.36.243:27019 :: caused by :: Connection refused”