Apple Developers Program "Certificates, Identifiers & Profiles" - is empty
This same thing has happened to me twice now. There's a delay between the time that you renew your membership and when your account is activated. If you wait approximately 30 minutes from the time you renew your subscription, and refresh the ios certificate page on developer.apple.com, your certificate will magically show up.
I just went through this like an hour ago. It was sure be rad if apple would at least explain wtf is going on after you re-submit your yearly fee.
I've come to this before, well I'd think anyone who has either just purchased a subscription of the developer program or in need to renew after paying for the new year.
To fix your problem you just need to follow the steps of creating a certificate. Then once you have created a new certificate you must go to each provisioning profile and renew each one bc they will lost a expired. To fix this you just hit edit and select your new certificate.
I advice to create certificate on one machine then in Xcode export the profile to all other machines by going to Xcode Preferences > Accounts and clicking on your account then exporting. With a passcode is a good idea. Of course before exporting see if creating a certificate solved the issue :)
Hope this helps :)