Works for me without any issues on the first try (and very fast!):
Did you make sure you downloaded the latest version of all tools you use? Specially for java it can quickly happen to use an outdated version. From their instructions at least Java 8 is required. I am currently running Java 10 (OpenJDK).
Their docs also state:
Please be aware that it is required that you have BuildTools #35 or later, older versions will not work
So you should make sure you also have the appropriate version of the tools (which I expect since 35 seems to be really old).
Usually 5XX errors indicate server side errors. Maybe they had some config or network issues on their end. Therefore it might work if you'll try it again after waiting a little while.
Maybe just some network node on the way to their servers broke. Apart from waiting and to try again you could try to setup a VPN to route the traffic throgh to avoid this failure (or turn it off in case you're using some!).
Maybe it's also worth to check your firewall (or proxy) settings.
PS: I was using git bash also on a Win 10 machine.
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