Power BI Service - Data source credentials

Hello Microsoft Power BI Community,

I'm having trouble connecting Data source credentials through Power BI Service. The web contents works fine on Power BI Desktop, my API endpoint GET takes two Oauth and grabs its access token to obtain the data. I tried both manually inputted credentials or inside of the parameters. The error is either Failed to update data source credentials: The underlying connection was closed: An unexpected error occurred on a send or Unable to connect to the remote server. I also have premium workspace, trying to use schedule refresh but Data source credentials is a current issue. Please advice what should be done!