Azure Cognative Services - api not working...

coding in M Query language...

My code to create a custom translation function:

let
Source = Web.Contents("https://api.cognitive.microsoft.com/sts/v1.0", [Headers=[#"Ocp-Apim-Subscription-Key"="xxxxxxx"]])
in
Source

My result:

404 Error Resource Not found.....

DataSource.Error: Web.Contents failed to get contents from 'https://api.cognitive.microsoft.com/sts/v1.0' (404): Resource Not Found
Details:
DataSourceKind=Web
DataSourcePath=https://api.cognitive.microsoft.com/sts/v1.0
Url=https://api.cognitive.microsoft.com/sts/v1.0

I have tried many other names for the api key [Header]:
apikey
apitoken
Authorization

Why is the resource not found?

In Azure, the subscription gave me the url which I copy and pasted. I see other users using this URL - they have also had problems connecting.

I chose "Anonymous" authentication, as has been indicated.