I'm using 184.108.40.206.0-20180220134543 and am connected to my 12.1 cloud DB in the same format as you are doing there. You're right that It is the same format as SQL Developer. If it was able to connect and you'd got the un/pw wrong then you do get a message saying that, so it does look like it's not even connecting that far. I can make mine get the same error if I deliberatly break it ( setting the port to the wrong number for example ). Have you triple checked the bits you've scribbed out on the screenshot??
Yes, they are exactly the same. Do I need to have an SSH tunnel open on port 1521 perhaps? SQL developer has a built in SSH tunnel option that I used to get that running. I assumed that the tunnel that I opened opened there would transfer over to Data Viz, but that might not be the case (I had SQL Developer and Data Viz open at the same time).
I believe I solved the problem. It turns out that there where network security settings within the cloud service itself that prevented me from linking Data Viz to my database. Once I made changes to the security rules I was able to connect. Good to know!