httpClient.GetStreamAsync System.NotSupportedException: The 'data' scheme is not supported

I am trying to save on server an image that is captured with Html2Canvas on Client.

The URL of the image is retrieved in javascript code from

html2Canvas.toDataURL("image/png");

and is sent to the server where I try to get the stream with

await httpClient.GetStreamAsync(imgUrl);

But I am getting the following error

System.NotSupportedException: The 'data' scheme is not supported.

The url has the following format

data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAByA..

Any idea about this?