But what posts did you look at and what have you already tried.
So we can narrow down the options on what else to try.
ECONNREFUSED means you tried to make a connection to another host but your connection was refused - either no one was listening or a firewall blocked you.
Have a look at the proxy settings in Postman.
Speak to your networks team. If this is run from Windows, you may need to allow port 8000 within the local firewall as it will probably be blocked by default.
Next thing is to look at is http vs https. Will the local end point actually accept http? It looks like a signup end point which ideally should be secure\https.
What happens if you try and access the end point via a standard browser? or from the command line\CURL. This can help pinpoint if the issue is with a setting in Postman or a more general issue (proxy\network\firewall). When in the request, in the right hand side pane, there is a code snippet option which can generate a CURL command from your request for this purpose.
Are there any other end paths for this application that you can test rather than sign up. Do any of them work?