Hello @WeylandZ! The Apple certificates are a RSA certificate composed by two parts: the private certificate and the public certificate. A .p12 file exports both certificates parts in a single file with a password. The private part of the certificate was created, from your KeyChain, when you've made the certificate requested on Apple Developer website and the public part of the certificate is created on this requesting flow and got available to download (and install on your KeyChain) once it finish. That way you might have on your Keychain the public and the private certificates together. So, if you are exporting a .p12 file from your KeyChain that contains both private and public parts of the RSA certificate, setting a password and sharing it with who will manage the app after you, you're done. Other solution is to revoke the certificate you've created and let whoever is gonna manage the app after you to create another certificate. I hope I could help.

Same here, I still didn't find a fix...

@sion.jw rebooting my macOS did the trick too, thank you!