when I try to download the Mozilla VPN on my desktop iMac it keeps saying installation failed

Quoting from Is Mozilla VPN compatible with my device? — "macOS (version 13 and up)" … You might be able to get an older copy for slightly older macOS, but I'm afraid there's none supporting your macOS 10.12.x unfortunately.

If the only device you are trying to use the standalone subscription based Mozilla VPN app on is a old Mac with macOS 10.12 then you can ask for a refund.

Also on download page it says VPN for Mac version 13.0 and up meaning macOS 13.0 and later. https://www.mozilla.org/products/vpn/download/

https://support.mozilla.org/en-US/kb/how-do-i-request-refund-mozilla-vpn

Hi,

Mozilla VPN is one of Mozilla's premium products. In order to get premium support from a dedicated agent, please submit your question with your Mozilla VPN app by going to Settings > Help > Contact Support. Alternatively, you can sign in to the Mozilla account connected to your subscription here (if not already) and then use this link.