Data source credentials for Power BI REST API - 404

Hello, 

I am building a report for my Power BI Admin needs. 

The report is done in Desktop and I am now trying to refresh the dataset it in the service. 

However I am getting an error for the Power BI REST API URL and I am not able to find a solution. 

This is the error I get : 

Below an example of a query I built where I call the API. 

I imagine the problem comes from the relative path I am using which Power BI Service seems to not be able to resolve the relative part. However I would like to keep this behaviour I reference the query above to get a major part of the info I need. 

Do you have an idea how I can solve this issue ? 

Thanks a lot !