This was intended as a comment, but it's too long, hopefully it will give you some hints.
Right now I don't have a mac to try OSX configs, but this is what I have now:
GPG is just an implementation of the PGP encryption standard, you can read more about it here; gpg keys can be a real pain, particularly on Windows, maybe try downloading the key and then using M-x package-import-keyring from within emacs to load the key manually?
I encountered this issue. I solved it using the following steps in order:
Make sure that the folder c:/Progra~2/GnuPG/bin is on your path before any other installed versions of the GnuPG executables (in my case, I had it installed via msys2).
Note that Progra~2 expands to "Program Files (x86)" on my system (I am using the 64 bit version ...