Distribution certificate / private key not installed

Question

Using Xcode 9.1, after building an iOS app, I want to archive it and upload it to the appStore for beta-testing. But I get the following issue after clicking the button

Answer 1

This answer is for "One Man" Team to solve this problem quickly without reading through too many information about "Team"

Step 1) Go to web browser, open your developer account. Go to Certificates, Identifiers & Profiles. Select Certificates / Production. You will see the certificate that was missing private key listed there. Click Revoke. And follow the instructions to remove this certificate. Step 2) That's it! go back to Xcode to Validate you app. It will now ask you to generate a new certificate. Now you happily uploading your apps.