Q: INSTALL_ERROR_DISTRIBUTION_SIGNED_BY_APPLE

Please post an EtreCheck report of your system. We can then look for obvious issues. Please click the link, download the app and run the report. Once you have the report, please copy and paste it to your reply to this post.

If you would like more info on what EtreCheck is, simply click the link and you will find a description of the app.

Open System Preferences > Date & Time. Confirm the system clock, time zone, and location are all correct.

I recommend selecting the option to set time and date automatically using one of Apple's time servers.