Forticlient VPN endend prematurely

I ran into the same “installation ended prematurely” issue with FortiClient VPN. What fixed it for me was running the installer as admin, clearing leftover Fortinet registry entries, and disabling antivirus temporarily. Also, make sure you're using the correct version (standard vs. EMS). If it keeps failing, try extracting the MSI and installing via command line for better error visibility.

What help me was deleting a file under ProgramData, it was the following:
C:\ProgramData\Applications\Cache\{15C7B361-A0B2-4E79-93E0-868B5000BA3F}\7.4.3.1790\FortiClientVPN.msi
Although the value in the {} might be different, but as long as its the folder containing the FortiClientVPN.msi , then deleting it should allow it to install properly. 
This is an issue common with ARM64 windows PCs, and that's what I’m on. This may not fix it if you’re having this error on a different architecture