Help... please! Credentials are required to connect to the Web source: Basic Authentication for REST

Hi there,

I have a set of REST Services that I connect to using Web.

The REST Services use Basic Authentication over HTTPS.

When refreshing these services through Power BI Desktop and entering the credentials for Basic Authentication, the data is refreshed correctly with no issue.

I then publish the Power BI report to Power BI Service and I try to set up the Schedule Refresh.

In Data Source Credentials I get the following:
Your data source can't be refreshed because the credentials are invalid. Please update your credentials and try again.

When I edit the credentials for Web, select Basic as the Authentication Method and enter the correct User Name and Password I get the following:
Failed to update data source credentials: Credentials are required to connect to the Web source.

If I try and hit the REST Service through a borwser and enter the exact same User Name and Password I am authenticated and the web service returns the expected result.

The REST Service is an HTTPS service that is publically accessible.

I have tried everything including switching authentication mechanisms and I even tried to download the Data Gateway to set that up. When I download the Data Gateway and click the EXE nothing happens. I have tried unblocking the EXE, running it in Compatibility Mode and still nothing.

Help... please!