I'm trying to upload my iOS app archive to iTunes Connect using Xcode, but when I click "Upload to App Store" I get the error that "Xcode attempted to locate or generate matching signing assets and failed to do so because of the following issues. Missing iOS Distribution signing identity for _____. Xcode can request one for you." I'm really confused, because I had literally just successfully uploaded an archive for the same app about 2 hours earlier, and then I needed to make one simple fix and then needed to reupload the archive, and now I'm getting this error. I literally did not touch anything else. I've done everything that I can think of to try fixing the problem, I restarted Xcode, my computer, went to Xcode preferences to click 'Download All' on the provisioning profiles, clicked "Reset" on the iOS Distribution on the same page, redownloaded the iOS distribution profile from the member center, went to the code signing settings in my app's build settings and manually set the release signing identity to the iOS distribution profile, and rearchived several times. Nothing is working. Help!
Edit: Here's the link about the expiring WWDRCA: https://developer.apple.com/support/certificates/expiration/
This is also confusing, because my app is just a normal iOS app that doesn't fit in any of those categories of people that need to take action. :S
I don't even know how to install the new certificate that they have a download link for. Just get "The System Roots keychain cannot be modified." in Keychain Access...