Power BI (on promise) change HTTPS to HTTP -- getting 503 error code

I'm trying to connect Power BI (on promise) to my OData service (using OData feed)

I use my secured environment - URL include HTTPS.

Power BI resolves my URL and replace the HTTPS to HTTP and I get 503 error code.

This is the error (

DataSource.Error: OData: Request failed: The remote server returned an error: (503) Server Unavailable. (503 Service Not Available

Sun Sep 29 09:36:01 2019
)
Details:
DataSourceKind=OData
DataSourcePath=http://rafed.xxx.xx/sap/opu/odata/sap/ZSD_Milestone_Information_CDS/ZSD_Milestone_Information
Url=http://rafed.xxx.xx/sap/opu/odata/sap/ZSD_Milestone_Information_CDS/ZSD_Milestone_Information?$top=1000

) 

Note: xxx means I have removed some poarts of the link for privacy reasons. 

any idea how to solve it? How to configure Power BI to use HTTPS without changing it to HTTP?