iOS icon upload iTunes connect: No alpha channels or transparencies
The iTunes connect specifically says that the app icon cannot contain alpha channels or transparencies. Though you can create an image without any transparencies easily, it is hard to create one without alpha channels. The open source Inkscape software that I use always exports .png images with alpha channels. Here is an easy way to overcome this problem using MAc's own image preview software.
Creating images without alpha channels with Mac image preview
Open the image in image preview app
Go to file - export
Select the format to PNG and uncheck the ALPHA checkbox