I went to sign my DMG and in the settings clicked the dropdown menu.
I was expecting the see the Developer ID Installer certificate available but the only one I saw was my Developer ID Application, so I just used that one.
Why isn’t the Developer ID Installer available - I thought it would be more appropraite?
Also, I got an initial error:
unable to build chain to self-signed root for signer Developer ID Application
But, I looked at my keychain and changed Trust from Always Trust, to Use System Defaults and it worked.