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

Add a new Production Certificate here, then download the .cer file and double click it to add it to Keychain.

All will be fine now, don't forget to restart Xcode!!!