I am submitting an iOS app to the App Store using Application Loader, however, it never gets past the \"Sending API usage to iTunes Connect\" stage. There i
I solved only rebooting mac.
I'm still searching for a less drastic solution!
You can solve this with a different approach using your iPhone. Disconnect ethernet internet cable connection (if you have one) and/or switch off wifi connection on your mac. Switch off your iPhone's wifi connection so G3 or G4 is active and turn on personal hotspot. Connect your iPhone with a usb cable with your computer and check in System Preferences -> Network if you're connected to internet via usb with iPhone. Start delivering your app with Application Loader program on your computer via your iPhone's internet connection. And yes you will cross the “Sending API usage to iTunes Connect” barrier and you will be able to upload the package to the iPhone store. At least I was!
If your Mac is has both a WiFi and an Ethernet connection, try turning off WiFi. That solved the problem for me (this time anyway).
I was connected to a VPN, disconnected and problem was solved.
Are you using Xcode Organiser > Upload to App Store or Application Loader?
I found I had the same issue when going though Xcode Organiser so tried it from the Application Loader (found within Xcodes application files) and it worked just fine. If that doesn't work there is a detailed activity log you can check to get a more detailed error.
Other things to try - check your firewall settings, maybe temporary disable them. - use an alternative connection, another wifi hotspot if you are on a MacBook, if not do what Oliver said and use your iPhone's cellular data.
Turning off iphone's wifi worked for me