Maven repositories are disabling HTTP support for security. Even though Nix adds some security with its own hash validation, broken mirrors are a, well, suboptimal experience. I don't know of any plans by sonatype, but it seems like a matter of time. https://www.lightbend.com/blog/lightbend-to-require-https-on-repos-starting-august-5-2020
Do not refer to <nixpkgs> as it will produce the following message: "evaluation aborted with the following error message: 'Illegal use of <nixpkgs> in Nixpkgs.'"