Y'all didn't zip up the game and upload it correctly. You're supposed to zip everything that was built (not just the .exe) For example my zip file for windows include:
- GameName_Data folder
- MonoBleedingEdge folder
- GameName.exe
- UnityCrashHandler32.exe
- UnityCrashHandler64.exe
- UnityPlayer.dll
You might not have all the same files, but you need to include all the files that Unity built for you. You can test this locally by unzipping in another location and running it. Feel free to reply to this comment once you've fixed it so I can leave feedback :)