I needed to create a new distribution certificate to upload my app to test flight. to do this, I created a certificate request via the keychain access tool. I then went to the Apple developer portal and created a distribution certificate by uploading that request. I then downloaded the certificate and added it to the keychain. When I attempt to upload, I get the missing key message:
"[name] has one Apple Distribution Certificate but its private key is not installed..."
How is this possible if I am on the computer that generated the request?