Hello,
I just ran the scenario myself using a WebService Key in OnPrem v17.3 and it does seem to work fine. A couple of things are required here:
1. Basic Authentication in Excel = Basic Authentication as authentication type on the NST instance
2. SSL cert as I am using https
3. ODataV4 endpoint must be enabled, OData SSL is enabled and OData itself is enabled
4. Note that I used page 20, not 21
Within Excel, I am using Advanced properties so I can configure the key plus user name, etc.
Hope it helps.
Thanks.