Hi,
the current installer has a bug that prevents it from running on NixOS.
It has a hardcoded path for chmod. It is only looking for it in "/bin/chmod". On NixOS this should either be a direct reference to the intended version within the /nix/store/ (that is what would be expected for a properly packaged package). Or within /run/current-system/sw/bin for anything looking for it through $path at runtime (discouraged but this is what everything that hasn't been packaged for NixOS specifically would end up using).
On NixOS the only file within /bin is "sh".
(Workaround for now: create a symlink for chmod within /bin; Or use the native NixOS package)