Why is Mininet error displayed when dumping from switch dpctl: failed to send packet to switch: Connection refused?

Question

IT education

Downloaded and installed on virtual machine. Everything would be fine, but there is at least one problem: I launched a mininet, a network was formed, and now I wanted to see a dump from the switch in this virtual network. Well, as it is written in the tutorial on the mininet website, I enter dpctl dump-flows tcp:127.0.0.1:6634 (I enter this into xterm, which separately displays switch s1) and as a result it gives me an error dpctl: failed to send packet to switch: Connection refused .