Why can't I retrieve the .deb files anymore

Navio / Edge Flight stack
2

There’s been some maintenance work that could possibly result in this kind of an error. Either way, there’s two ways to overcome the problem

  1. Change https to http.
  2. Use the method described in this post.

In case you removed you rapm-navio2 package beforehand you can just sudo apt-get install apm-navio2, then.