Hey, sorry for responding so late
Basically the message "Some game files are missing or corrupted" indicates that one or more files have been modified or they're missing. Basically the game has a list of all file hashes (based on how the files were downloaded from the server) and checks the hashes for every file upon start.
This behaviour can be disabled in the launcher options by ticking the "Disable file check" option. However, it sounds like there are some download issues, resulting in corrupted files. If you get the error Failed to load il2cpp, this indicates that some core files are either missing or corrupted.
Troubleshooting this is a bit difficult unfortunately... usually it's either caused by a firewall or anti virus program, or a connection issue. Do you use a wired or wireless (wifi) connection?
It could also be related to the ISP (e.g. a routing issue). We only have a single server unfortunately (it's located in Germany).
If nothing works, I could give you a Steam key alternatively (so you could download the game through Steam)