Hello,
I've recently upgraded to Apple's latest beta version, macOS 10.15 Catalina, which is due to be launched in Autumn 2019. As I tried to install a fresh download of the (UK English) Millie voice from Cepstral (I have it licensed for personal use), currently still at version 6.2.3.685), getting it from the usual download page (https://www.cepstral.com/en/personal/download), I got an error saying that the certificate with which the macOS package had been signed with had expired (and, indeed, viewing that certificate showed that Cepstral let it expire on Wednesday, 2 August 2017 at 21:09:11 Western European Summer Time). The actual files inside that package are from... 2013!
You can 'force' the install in spite of the macOS complaints, but eventually, it will ultimately fail with the message: The package “Cepstral_Millie_macosx_6.2.3.685.pkg” is untrusted. Because I cannot attach images to this post, I've done a screenshot and uploaded it to one of my own servers.
Does anyone have an alternate link from Cepstral with a more recent version of the Millie voice?