Failing upload is usually a sign of an issue with the internet connection or with certain plugins. Have you tried using a different internet connection of possible? Have you tried using a different browser to rule out the plugins issues?
The red dots on the uploader coverage map are places where the aircraft was not flying straight with the respect to the previously collected image. If there are more than 30% of these images it is determined that the aircraft was not flying forwards for the majority of the flight and the upload will not be allowed.
You can use the Classic workflow with any aircraft. It is just informing you that the DJI workflow is preferred.