Seems like the nixpkgs commit doesn't exist anymore.
error: unable to download 'https://api.github.com/repos/NixOS/nixpkgs/tarball/5f862a767195f5183b2aca3618b45b9a8d1ed9d6': HTTP error 404
response body:
404: Not Found
… while fetching the input 'github:NixOS/nixpkgs/5f862a767195f5183b2aca3618b45b9a8d1ed9d6'
Seems like the nixpkgs commit doesn't exist anymore.