Scheduled Refresh - Query contains unsupported function. Odbc.DataSource

I'm working a case with Microsoft Support that deals with this very issue.

Here is what you're likely running into: some functions are ONLY supported in the Power BI service if the first parameter (i.e., URL) is hardcoded. If you use a variable or an expression it is not supported.

This is what I was told on 2/10/2020:

I have an update from the product team and they identified the issue.

let
    Source = (CitPmoProjectSiteUrl as text, ListType as text) => let
        Source = SharePoint.Tables(CitPmoProjectSiteUrl, [ApiVersion = 15]),
        Issues = Source{[Title=ListType]}[Items]
    in
        Issues,
in
    Source

The highlighted one is not  a valid connection string but it points to a variable which is a valid connection string. Now Sharepoint.Tables looks for a valid connection string instead of a variable  which is why  it says  unsupported function .

I have found this restriction applies to, at least, SharePoint.Tables(), OData.Feed(), and, apparently, the call you're using as well.

I will be speaking again with them about this on Monday, 3/2. If I receive helpful information I'll share it here.