Custom Data Connection Returns JSON But Desktop App Says OData Not Service or Feed

I've been working on a custom data connector for Power BI desktop that consumes data from a REST API we've built that is secured by Azure AD.  I thought I was finally through the hard part - getting the authentication working - but now that I'm connecting to our REST API and retrieving data, I'm getting the error from Power BI Desktop of "OData:  The given URL neither points to an OData service or a feed."  

When I look in Fiddler though, I can see data coming back, and it's all correctly formatted JSON.  I copied the data from Fiddler and pasted directly into a Visual Studio JSON document and it shows no errors at all.  So...I'm not really sure what Power BI wants here.  My feed is configured in my custom data connector like this:

source = OData.Feed("https://www.foo.com/api/data/powerbisummarydata")

The only thing I could think of was that perhaps "OData.Feed" isn't the right option, but I could not find another one in the SDK that would appear to work.  Any suggestions?  I've been looking through the MyGraph sample as well in the SDK samples and cannot find anything it's really doing differently.

Thanks.