Realtime Push URL returning 401 from app integration (though works fine from cURL)

Hi!

I am trying to setup an integration with Power BI Service for ingesting real time data. I have configured the data set and a dashboard as per the documentation.

When I test using cURL (with the provided code when setting up the API) it works fine - i see the data populated into the dashboard. However when I use the push URL in my application I can see the data going out, but getting a 401 from PowerBI - I have compared the headers, URL and everything looks fine. I can't for the life of me work out what is causing the 401

as per https://docs.microsoft.com/en-us/power-bi/connect-data/service-real-time-streaming 

"For streaming datasets created using the Power BI service UI, as described in the previous paragraph, Azure AD authentication is not required. In such datasets, the dataset owner receives a URL with a rowkey, which authorizes the requestor to push data into the dataset with out using an Azure AD OAuth bearer token. "

as such the URL with embedded key should be enough (and indeed, with cURL it is) - is there any way to debug why I am getting this issue? does anyone know why this issue is occurring?