Error ITMS-90717: "Invalid App Store Icon"

The below solution worked for me

1. Click & open the App Store icon (1024*1024) in the preview app.
2. Export it by unticking the Alpha channel.
3. Replace the current App Store icon with the newly exported icon image.
4. Validate and upload.

Note: This will not work on Mac OS High Sierra, please try a lower version to export without alpha or use any one of the image editing applications or try out the below alternatives.

Alternative 1: (Using Sierra or High Sierra and Ionic)

1. Copy and Paste the App Store icon to the desktop.
2. Open the image. Click File Menu->Duplicate.
3. Save it by unticking the Alpha channel.
4. Replace the current App Store icon with this one.
5. Validate and upload.

Alternative 2: If duplicate does not work, try doing opening it in preview and then doing file export. I was able to unselect the alpha channel there. – by Alejandro Corredor.

Alternative 3 : Using High Sierra and Ionic, found the problem image in the following folder: [app name]/platforms/ios/[app name]/Images.xcassets/Appicon.appiconset/icon-1024.png. We have to copy it to the desktop and Save As while unchecking Alpha, then rename it to icon-1024.png, then delete the original and copy the new file back to the original folder. Export did not work though no error was displayed and all permissions were set/777. Hope this helps save someone the day I just lost. – by Ralph Hinkley

I faced the same problem and wasn't able to fix it with the provided solution by Shamsudheen TK. Ionic somehow added transparency to my icons even if the source icon did not have any transparency at all. In the end I was able to resolve it by:

Install imagemagick (MacOS):

brew install imagemagick

Remove alpha channel from all images in resource folder:

find ./resources/ -name "*.png" -exec convert "{}" -alpha off "{}" \;