I am getting this error while trying to launch pgAdmin4
Failed to connect to the server: “Connection refused” - request URL: 127.0.0.1:39595/misc/ping?key=90f45e1-de96-47da-ac9d-459ababbb365"
Better check their documentation
From your error i gather that it seems like pgAdmin4 can not connect to the local port PostgreSQL, or is that something else you try to access?